diff --git a/hiero-enterprise-base/src/test/java/com/openelements/hiero/base/test/FileClientImplTest.java b/hiero-enterprise-base/src/test/java/com/openelements/hiero/base/test/FileClientImplTest.java
index a8ba70bf..e48f1fc1 100644
--- a/hiero-enterprise-base/src/test/java/com/openelements/hiero/base/test/FileClientImplTest.java
+++ b/hiero-enterprise-base/src/test/java/com/openelements/hiero/base/test/FileClientImplTest.java
@@ -5,6 +5,8 @@
 import com.openelements.hiero.base.implementation.FileClientImpl;
 import com.openelements.hiero.base.protocol.FileCreateResult;
 import com.openelements.hiero.base.protocol.FileCreateRequest;
+import com.openelements.hiero.base.protocol.FileUpdateResult;
+import com.openelements.hiero.base.protocol.FileUpdateRequest;
 import com.openelements.hiero.base.protocol.FileAppendRequest;
 import com.openelements.hiero.base.protocol.FileAppendResult;
 import com.openelements.hiero.base.protocol.FileInfoRequest;
@@ -120,6 +122,104 @@ void testCreateFileThrowsExceptionForNullContent() {
         Assertions.assertTrue(exception.getMessage().contains(message));
     }
 
+    @Test
+    void testUpdateFile() throws HieroException {
+        // mock
+        final FileUpdateResult fileUpdateResult = Mockito.mock(FileUpdateResult.class);
+
+        // given
+        final FileId fileId = FileId.fromString("1.2.3");
+        final byte[] updatedContent = "Hello Hiero! Updated".getBytes();
+
+        // then
+        when(protocolLayerClient.executeFileUpdateRequestTransaction(any(FileUpdateRequest.class)))
+                .thenReturn(fileUpdateResult);
+
+        fileClientImpl.updateFile(fileId, updatedContent);
+
+        verify(protocolLayerClient, times(1))
+                .executeFileUpdateRequestTransaction(any(FileUpdateRequest.class));
+    }
+
+    @Test
+    void testUpdateFileForSizeGreaterThanFileCreateMaxSize() throws HieroException {
+        // mock
+        final FileUpdateResult fileUpdateResult = Mockito.mock(FileUpdateResult.class);
+        final FileAppendResult fileAppendResult = Mockito.mock(FileAppendResult.class);
+
+        // given
+        final FileId fileId = FileId.fromString("1.2.3");
+        final byte[] updatedContent = new byte[FileCreateRequest.FILE_CREATE_MAX_SIZE * 2];
+        // -1 because 1 for executeFileCreateTransaction()
+        final int appendCount = Math.floorDiv(updatedContent.length, FileCreateRequest.FILE_CREATE_MAX_SIZE) - 1;
+
+        //then
+        when(protocolLayerClient.executeFileUpdateRequestTransaction(any(FileUpdateRequest.class)))
+                .thenReturn(fileUpdateResult);
+        when(protocolLayerClient.executeFileAppendRequestTransaction(any(FileAppendRequest.class)))
+                .thenReturn(fileAppendResult);
+
+        fileClientImpl.updateFile(fileId, updatedContent);
+
+        verify(protocolLayerClient, times(1))
+                .executeFileUpdateRequestTransaction(any(FileUpdateRequest.class));
+        verify(protocolLayerClient, times(appendCount))
+                .executeFileAppendRequestTransaction(any(FileAppendRequest.class));
+    }
+
+    @Test
+    void testUpdateFileThrowsExceptionForInvalidFileId() throws HieroException {
+        final String message = "Failed to execute transaction of type FileUpdateTransaction";
+
+        // given
+        final FileId fileId = FileId.fromString("1.2.3");
+        final byte[] updatedContent = "Hello Hiero! Updated".getBytes();
+
+        // then
+        when(protocolLayerClient.executeFileUpdateRequestTransaction(any(FileUpdateRequest.class)))
+                .thenThrow(new HieroException(message));
+
+        final HieroException exception = Assertions.assertThrows(
+                HieroException.class, () -> fileClientImpl.updateFile(fileId, updatedContent)
+        );
+        Assertions.assertTrue(exception.getMessage().contains(message));
+    }
+
+    @Test
+    void testUpdateFileThrowsExceptionForSizeGreaterThanMaxFileSize() {
+        final String message = "File contents must be less than " + FileCreateRequest.FILE_MAX_SIZE + " bytes";
+
+        // given
+        final FileId fileId = FileId.fromString("1.2.3");
+        final byte[] updatedContent = new byte[FileCreateRequest.FILE_MAX_SIZE + 1];
+
+        // then
+        final HieroException exception = Assertions.assertThrows(
+                HieroException.class, () -> fileClientImpl.updateFile(fileId, updatedContent)
+        );
+        Assertions.assertTrue(exception.getMessage().contains(message));
+    }
+
+    @Test
+    void testUpdateFileThrowsExceptionForNullArguments() {
+        // given
+        final FileId fileId = FileId.fromString("1.2.3");
+        final byte[] updatedContent = "Hello Hiero! Updated".getBytes();
+
+        // then
+        final NullPointerException nullContentException = Assertions.assertThrows(
+                NullPointerException.class, () -> fileClientImpl.updateFile(fileId, null)
+        );
+        Assertions.assertTrue(nullContentException.getMessage().contains("content must not be null"));
+
+        final NullPointerException nullIdException = Assertions.assertThrows(
+                NullPointerException.class, () -> fileClientImpl.updateFile(null, updatedContent)
+        );
+        Assertions.assertTrue(nullIdException.getMessage().contains("fileId must not be null"));
+
+        Assertions.assertThrows(NullPointerException.class, () -> fileClientImpl.updateFile(null, null));
+    }
+
     @Test
     void testGetFileSize() throws HieroException {
         // mocks
diff --git a/hiero-enterprise-spring/src/test/java/com/openelements/hiero/spring/test/FileClientTests.java b/hiero-enterprise-spring/src/test/java/com/openelements/hiero/spring/test/FileClientTests.java
index 84bcb429..3289c70b 100644
--- a/hiero-enterprise-spring/src/test/java/com/openelements/hiero/spring/test/FileClientTests.java
+++ b/hiero-enterprise-spring/src/test/java/com/openelements/hiero/spring/test/FileClientTests.java
@@ -3,6 +3,7 @@
 import com.hedera.hashgraph.sdk.FileId;
 import com.openelements.hiero.base.FileClient;
 import com.openelements.hiero.base.HieroException;
+
 import java.time.Duration;
 import java.time.Instant;
 import java.time.temporal.ChronoUnit;
@@ -147,9 +148,9 @@ void testDeleteFileByFileId() throws Exception {
     @Test
     void testUpdateFileByFileId() throws Exception {
         //given
-        final byte[] contents = "Hello, Hedera!".getBytes();
+        final byte[] contents = "Hello, Hiero!".getBytes();
         final FileId fileId = fileClient.createFile(contents);
-        final String newContent = "Hello, Hedera! Updated";
+        final String newContent = "Hello, Hiero! Updated";
 
         //when
         fileClient.updateFile(fileId, newContent.getBytes());
@@ -159,6 +160,55 @@ void testUpdateFileByFileId() throws Exception {
         Assertions.assertArrayEquals(newContent.getBytes(), readContents);
     }
 
+    @Test
+    void testUpdateFileForSizeGreaterThanCreateFileSize() throws HieroException {
+        // given
+        final byte[] contents = "Hello, Hiero!".getBytes();
+        final FileId fileId = fileClient.createFile(contents);
+        final byte[] updatedContent = new byte[FileCreateRequest.FILE_CREATE_MAX_SIZE * 2];
+
+        // when
+        fileClient.updateFile(fileId, updatedContent);
+
+        // then
+        final byte[] readContent = fileClient.readFile(fileId);
+        Assertions.assertArrayEquals(updatedContent, readContent);
+    }
+
+    @Test
+    void testUpdateFileThrowExceptionForInvalidFileId() {
+        // given
+        final FileId fileId = FileId.fromString("1.2.3");
+        final byte[] updatedContent = "Hello, Hiero! Update".getBytes();
+
+        // then
+        Assertions.assertThrows(HieroException.class, () -> fileClient.updateFile(fileId, updatedContent));
+    }
+
+    @Test
+    void testUpdateFileThrowExceptionIfSizeExceedMaxSize() throws HieroException {
+        // given
+        final byte[] contents = "Hello, Hiero!".getBytes();
+        final FileId fileId = fileClient.createFile(contents);
+        final byte[] updatedContent = new byte[FileCreateRequest.FILE_MAX_SIZE + 1];
+
+        // then
+        Assertions.assertThrows(HieroException.class, () -> fileClient.updateFile(fileId, updatedContent));
+    }
+
+    @Test
+    void testUpdateFileThrowsErrorForNullValues() throws HieroException {
+        // given
+        final byte[] contents = "Hello, Hiero!".getBytes();
+        final FileId fileId = fileClient.createFile(contents);
+        final byte[] updatedContent = "Hello, Hiero! Update".getBytes();
+
+        // then
+        Assertions.assertThrows(NullPointerException.class, () -> fileClient.updateFile(fileId, null));
+        Assertions.assertThrows(NullPointerException.class, () -> fileClient.updateFile(null, updatedContent));
+        Assertions.assertThrows(NullPointerException.class, () -> fileClient.updateFile(null, null));
+    }
+
     @Test
     void testDeleteFileByStringId() throws Exception {
         //given