Gh0st’s UPMS Installer packs a collection of useful software tools for converting to & from a Pandora’s battery, writing the IPL to your memory stick, and creating the Ultimate Unbricker/Downgrader solution.

Easily achieve any of the following when combining both the Pandora battery and Ultimate Pandora Memory Stick (UPMS):

• Upgrade a Slim to 3.71-2 M33;
• Upgrade a Phat to 3.71-2 M33 w/ 1.50-2 kernel patch;
• Upgrade a Slim to 3.80-5 M33;
• Upgrade a Phat to 3.80-5 M33 w/ 1.50 kernel patch;
• Downgrade a Phat to 1.50;
• Upgrade a Phat straight to 3.52 M33 from Extended Boot Menu, then install update 4 via XMB — with no need to downgrade to 1.50;
• Boot the PSP using Ultimate Loader with support for choosing which Pandora you require — V1, V3, or V4;
• Boot to the XMB with the Pandora battery inserted (Phat Only);
• Boot to a full 1.50 firmware from the memory stick (Phat Only);
• Use PSP Filer and other tools;
• Upgraded a Phat or Slim to 3.71-4 M33 from the XMB with the update;
• Recover any bricked PSP (Phat or Slim).

Of course you’ll require the corresponding [official] firmware EBOOT(s) depending on your selection. Copy each EBOOT to the root of your memory stick — 1.50 (rename to 150.PBP), 3.71 (371.PBP), 3.80 (380.PBP), and also a second copy of 1.50 named “UPDATE.PBP.”

To start using UPMS Installer:

1. Ensure UMD Mode is set to “Sony NP9660.” Hold R-Trigger while booting to enter the recovery console, go to Configuration, and set the UMD Mode there.
2. Copy UPMSInstallerV3.cso to the ISO directory on your memory stick; i.e.) F:\ISO or /Volumes/PSP/ISO
3. Browse to the XMB game menu and launch.

Tutorial, other important info, and ongoing discussions concerning UPMS can be found here, and here. All software authors are properly credited.

Download:
UPMS Installer V3 (Sapphire)
Official PSP Firmware Updates

- source: upms-project.com