Custom Firmware 4.01 M33-2
The installation requires a PSP with 3.52 M33-3 or higher [fat PSP], or
3.60 m33 or higher [Slim PSP]. If you PSP(fat or slim) is on Offical sony firmwares, you
shouldn’t try it. Please ensure that your battery is at least 78% loaded ad Kernel access on 3.XX
Copy the UPDATE folder into /PSP/GAME. Run it, the update will be done by Sony updater. At the end when you are asked to reboot the PSP, press X or O(Remember to do it). Do not skip this step shutting down the PSP by yourself, or you’ll end with a brick. Then you can erase "UPDATE" folder, they won’t be any longer necessary.