how to i change the AI's skins???

ohk thanks bro.

Take a look in this toic :
http://www.lfsforum.net/showthread.php?t=26119

Here you can download a pack that let the AI cars have skins. Each AI have their skin, on each car. Pretty big pack, but contains 400 skins

a different way is to call a custom skin the name of the AI (i.e AI 1) and thee you go!