RenameFiles also moves files - vice versa it's old Unix tradition.
And RenameFileUTF8 hopefully converts your umlauts, Umlaute (or whatever) correct.
From LazFileUtils.xml:
RenameFileUTF8
Renames a file to the specified value
RenameFileUTF8 is a Boolean function used to rename a file to the specified new value.
For the Windows enviroment, MoveFileW is called to rename the file using the values
specified in OldName and NewName. For UNIX-like enviroments, DeleteFile in SysUtils is
called to delete the specified file name. InvalidateFileStateCache is also called.
The return value is True if the file is renamed successfully.
Winni