If you want to change your model, because you are bored of the old ones or just want to try new ones, with different sounds, then go here :
http://planetquake.gamespy.com/View.php?view=Modeloftheweek.List&category_select_id=3
Your model is visible only by yourself, so the others won't be able to see your custom model if they haven't downloaded yet. You could change one of the default models by yourself, but you should modify the scripts in the pak0 and 2.....you only need a program to open pk3 files and a program like photoshop... however that's another story
