much love to JaiaV at PSP Hacks for this tut.

Whenever you are using Hellcat's Recovery Flasher or the XGEN Updater V2 please make sure your battery is charged at least 75% or on the A/C adapter.

Both of these programs require that you already be running CFW. If you are running OFW please seethis tutorial by Scorpus.

If you're going to use any PSP game that requires 5.55+ (Gran Turismo etc) on either software, M33 or GEN, you'll need to decrypt it using the 5.55-6.00 decrypter. You'll need the decrypter and UMDgen.

Upgrade from 5.00 M33-6 to 5.50 GEN B-2

This one is fairly simple. There's no need to upgrade to any GEN CFW prior to using this updater. You can go straight to GEN B-2 without any in between from M33 CFW.

You'll need: XGEN Updater V2.

Open up the zip file you just downloaded. Copy the UPDATER folder into your X:/PSP/GAME folder and the 550.pbp into your MS' root X:/.

You may want to use Hellcat's Recovery Flasher to back up your settings. It's not a necessary step.

Run the XGEN installer from your XMB and select Flash Install CFW 5.50 GEN-B2. This will install said cfw to your psp. You're done.

Additional info: GEN B-2 disables the VSH menu. If you want to use VSH menu you will have to reboot your PSP while holding the R button to get to the recovery menu and enable the VSH menu inside of the Recovery's plugin menu. To use ISO/CSO you'll also have to re-enable M33 drivers for your UMD. To get some PSX games to run you'll need to update popsloader with this.

Downgrading from 5.50 GEN B-2 to 5.00 M33-6

For whatever reason, you don't want to use 5.50 GEN B-2 and want to go back to M33 based cfw. It's as easy as using Hellcat's Recovery Flasher to flash it right back on your psp.

Just download Hellcat's Recovery Flasher if you don't already have it and copy the RECOVERY folder into your X:/PSP/GAME folder. You'll need the OFW update pbp of whichever version of M33 you wanted to downgrade to, in this case 5.00. You can get that at 500.pbp. Rename the 5.00 OFW update to 500.pbp and copy the file to your MS' root directory X:/.

Now you just run Hellcat's Recovery Flasher from your XMB, making sure that whichever fw version you wanted is selected at the top, then select Install CFW. HCRF should replace 5.50 GEN B-2 with M33 cfw. Just wait until the program tells you to press any button to shutdown. Press a button and power on your PSP. Congratulations, you're back on M33 cfw.

This whole process, both upgrading and downgrading took me less than 10 minutes.

Tested multiple times with no errors of any kind on a PSP-2001 TA-085v2 motherboard.

And knowing that direct download links dont work in quotes HERES the link