What you need:

• a PSP with 3.90 M33-3 or higher. (Use this tutorial to update your psp to that firmware, if you don't already have it: 3.90 M33 Installation Guide
  
  

• The files below:
  
  
  
  
  Installation:

First download the files above and extract them
1. Plug the PSP into the PC and turn USB Connection on.
2. Copy the UPDATE folder from the 3.93 Custom firmware folder to the GAME folder (which is inside the PSP folder). So, the EBOOT.PBP should be in PSP>GAME>UPDATE>
4. Navigate to the root of the Memory Stick (Where you should have the MP_ROOT folder as well as the PSP, MUSIC, VIDEO folders.). Here, copy the 393.PBP file.
3. After disconnecting your PSP from USB, navigate to the Game menu on the PSP look for the 3.93Installer icon; it should be first. Press X to run it. It will not run unless there is 80 percent battery free.
4. Press X and the update process will start. Yes it may look similar to a regular Sony update but don't worry!
5. Once finished, the updater will ask you to press X or O to reboot. You MUST do this, otherwise you'll end up with a brick.
6. You've now successfully installed 3.93Custom Firmware  
7. Once the PSP has restarted, connect to USB again. Now, from the 3.93 Update 2 folder you extracted earlier, copy the UPDATE folder  into PSP>GAME>  [on your PSP]. It will ask you if you are sure you want to overwrite. Say yes. Then disconnect, go to the GAME menu, and run the Update2 program. Again, it should be the first one there. Press X, and you are done.

CHANGES:
--------

1. Uses the 3.93 kernel
2. Implented all the original custom firmware features.
3. Ability to use the normal recovery inside the XMB by pressing the HOME button:
- When in the recovery, the system is suspended, and you can change all options directly.
- All options work immediatly, there is no need to reboot (even the Slim's USB charging option)
- Ability to make a Pandora battery from the recovery, read and restore the EEPROM, etc. Providing that the motherboard supports it.
- Ability to hide the MAC adress in System Information, if you do so, the MAC will show visually as all 0's.
- Ability to save the savegames in normal format, rather then encrypted (only functions in March33 and Sony NP9960 mode).
4. The native 3.93 pops isn't as good as the previous pops, therefor I hope the popsloader will get updated to support 3.93.

Your PSP is now the latest custom firmware ;)