Seriously Sonnie theres no harm in opening it, you lose your warranty (if you stil have one) but whatever, When I had my phat (b4 i got slim) i opened it all the time to clean it. Just dont touch metal while touching the circutry, use anti-static spray and stuff, you dont wanna fry your psp.

Clean workspace with light, a lot of tiny screws, you dont want to lose them.
one more things GET THE RIGHT SIZE SCREWDRIVER, you dont wanna strip your screws.

I know theres also i site that shows u step by step (not youtube -.-) with like pics and stuff, something about llamas but idk.