to downgrade to fw 3.55 from any fw u need a hardware flasher. Tht's like a seperate harddrive which lets u successfully downgrade ur ps3. U have to open ur ps3 up to do it. Its not risky unless u have ADD and some other disease.Its called an e3 flasher. U could buy one 4 $40 ONLINE!!! However if u are wanting to hack mw2 just buy a shata cable and u could put patches on it w/o jailbreaking it. all u have to do is take the normal harddrive out and plug into ur cpu using shata cable. then u have to do random shit tht im not explainig. find it on google or youtube. HOPE I HELPED!!