shockwave

Hello I need help... I downloaded Optimus Prime skin mod that contents:optimus prime.dff,optimus prime.txd. I know that I have to do it by IMGtool but I don't know what file to replace.I tried player.dff and CJ was alien!! Do you know what file is CJ??? I JUST NEED TO REPLACE IT..HELP,HELP,HELP..

and when I want to replace CJ skin what file do I have to replace?]