well, since you already have cfw installed, then you dont need to use chickHEN or a pandora battery and mms. all you need to do is download official firmware 5.00 and the 5.00 m33-6 file and run it.
you can find both here:
Custom Firmware 5.00 M33-6 Released, PSP Hacks - PSP Slim Hacks
all you need to do is download ofw 5.00 and change the name to 500.pbp (if its not already called that). then download the 5.00 m33-6 file and unpack it.
there will be a folder named UPDATE after it is unpacked. you need to move the 500.pbp file into the UPDATE folder with the other eboot.
after that, just transfer the UPDATE folder to your psp and put it in the GAME folder. then start your psp and run the update. that should do it!