So I highly suggest that you visit their page, and make a donation so the M33 team can continue hacking the PSP.
It took me some time to figure out how to install this update on my PSP, because of a small misunderstanding.
The procedure to apply this patch is quite simple; just navigate into the applications menu and run the app called M33Update #4.
In a few seconds a message will tell you that your PSP has been patched successfully, and pressing X will turn off the PSP.
To save people a lot of work, I decided to write this tutorial which includes all the necessary files in one location.
But first we need to make sure that your PSP satisfies the basic requirements.
This is perfectly OK, because the M33 Creator is doing it’s work in the background. Look into the applications menu again, and you should see another application called the “M33 Upgrade 3.52”.Official Sony firmwares must be cracked and downgraded before upgrading to your own custom firmware.Unfortunately for you, you'll have to wait until someone figures out how to downgrade from official firmware 4.01 or higher.Finally you have upgraded your PSP to the latest and greatest custom firmware.Make sure to check back often for updates on M33 firmwares, and all-in-one packages!
When you download the Update #4 (M33-4) file from any of the PSP sites, it is not the installer.