Sorry for the dumb question, but how can one check what firmware the PSP uses?

I bought a used and a hackable PSP-2000 (G) that has been used with a Pandora battery and I want to hack it by using a custom firmware. The thing is, I've no idea what steps to take so that the PSP wouldn't brick since there're just too many guides around. I've read the majority of the threads from the Help and Tutorial and Guide section, but I still haven't got the slightest clue as to what firmware version I should update to, or what custom firmware I should use as the guides seem a tad outdated.

So yeah, any tips as to what firmware is the safest to use and how?