If you try to rename a file to a name that is the same, but in a different case within the home directory the function will fail. This is because now we are using shared storage for home directories, to maintain interoperability, 'FileName' and 'filename' are treated as the same file. This also means that you cannot have two variants of the same name within your home directory.
To work around this you will need to rename your file to something else, then back with the case you want, ie. 'filename' > 'filename~' > 'FileName'.
The "mv" function in a terminal will ask you if you wish to overwrite, by confirming, you will successfully be able to change the case of the filename you are changing.