How do you edit RES files? -1 reply

Hey, I am new to the whole modding "movement" and I making a mod which I attemped to create my mod in different forms for Call of Duty (Warrior: The Future War Against Terror). So in short how do you edit the game files to do a weapons selection similar to DoD's weapon without buying weapon selection system? Are they found in an RES file and how do you edit RES files? Thnx for any answers...