Go to /dev_hdd0/home/0000000x and delete the exdata folder (x is username number, if you just have 1 account on your ps3 it will be 00000001 and so on)
After all this it will ask to rebuild the registry, dlc will no longer be activated, and the PSN account will be gone from your system.
STOP! Before you ask questions... READ the first post! RTFFP = Read The F*cking First Post
Yes, A 3.55 "jb" (cfw) is available, no >3.55 "jb" or cfw yet.
Yes, A 3.55 downgrade is available. But not to lower than stock firmware! (What it came with)
No >3.55 downgrade is out there yet.