how to update the file in the dropbox with a different name but the contents of file are same - using iOS core API

I have used the below method to update a file,

- (void)uploadFile:(NSString *)filename toPath:(NSString *)path withParentRev:(NSString *)parentRev
    fromPath:(NSString *)sourcePath;

I want to update a file say abc.txt in the dropbox, with the same content but with different filename say def.txt. For this, I have get the parentRev of abc.txt and i have changed the filename to def.txt and uploaded the def.txt with the same parentRevision. But, the def.txt was uploaded as a separate file instead of replacing/updating the abc.txt. Now, the dropbox contains two files abc.txt and def.txt. Please tell me is there any way to replace the file abc.txt with def.txt. Thank you.