reprograming ignition key

I was wondering if anyone could help me out with this, I drive a 2002 GP SE, I lost my original key several years ago so I went to my dealership and got a new key and was able to program it without the original. Several months later I found the originals kept them as an extra set but never got around to reprogramming them. Now I lost my programed key:banghead: and just have the unprogrammed extra set. can anyone tell me the sequence that I have to do in order to reprogram my old set. or isn't it possible to change the program on programmed keys. any help would be greatly appreciated