Here's link on all guides on how to upgrade to firmware 5.00m33-6, 5.50 GEN and so on. Also including a guide on how to convert your Battery <-> Pandora Battery and Memory Stick <-> Magic Memory Stick.
Link : http://forums.qj.net/guides-psp-hacks-homebrew-emulators/162702-guide-ultimate-cfw-installation-guide.html