click on your windows button on the bottom left hand corner of your screen in the search line type %appdata% click on the roaming file click on the .rFactor file open the second file on the list which is a rfactor file and the file type is "name"(open with notepad if it asks you how to open it) They type your new nickname in there following the current format. I'm not sure exactly how that works since I can't remember but you'll figure it out. I'm sure there are other ways of doing it but that is the way I know how to.
