Here's what you got to do. This mini tutorial will get you to update to 5.00 M33-6.
(i have to use spaces in my url cos i cant post url links until i have 15 posts!)
-Download Hellcat Recovery Flasher from here h t t p : / / fserv.skill-club.com/get_959_7eae.html
-Download the official firmware 5.00 h t t p : / / w w w.megaupload.com/?d=1FC0QCPO
-Extract the hellcat recovery download and copy the recovery folder to PSP/GAME
-Extract the official firmware update and copy it to the root of your memory stick (not MP_ROOT)
-Shutdown your psp completely by pushing and holding the power button.
-Hold down the R button
-Select "game folder homebrew" and press X (this should change it to 3.10 kernel)
-Launch Hellcat Recovery flasher from the game menu
-Ensure "Target FW : 5.00" is selected and scroll down and press X against "Install CFW (of version selected above)
-Press X against "reset (format) settings as well"
-This will install custom firmware. (you might get some assigning flashes error)
-Once complete it will ask you to press X to shutdown
-After the shutdown, startup again and set your region and name of your psp
-Check you're on 5.00M3-6!