You need to copy the UI folder out into C:\Program Files\Activision\Rome - Total War\Data\ and rename the corresponding .pak file so that the game cannot find it, and looks in the UI folder. Personally I just add #$% to the beginning of the filename, that way I can easily revert if I do something wrong. Deleting game files is bad, in my experience. I will try to post something more specific tomorrow if it is still needed.