Click on the Firmware Updater in the XMB, it will download the EBOOT.PBP, it will look to see if you have the 500.PBP. If you don't, the Firmware Updater will download from your PSP. I suggest you don't download it, because it will take forever.
So download the 500.PBP here: http://rapidshare.com/files/154173870/500.PBP
After downloading the 500.PBP, plug your PSP into the computer via USB cable and cut/copy and paste it in ms0:/PSP/GAME/UPDATE. Then after that, disconnect the USB Connection and run the EBOOT.PBP from your XMB. It will not say EBOOT.PBP, I forgot what it says, but you will see an icon of a 5.00 M33-6 Update. Run the update, and just wait a couple minutes, and your done =P

Rep+ if this helped. And next time, don't post in here, it's the wrong section.