If i bought a psp slim refurbished from eb games website then do you know if the upgrade the firmware?

I basically wanna use custom firmware and want to know if they always 100% of the time will be 3.3 or if anyone knows how to downgrade 3.3 that would be great.
sorry i dont think 3.3 is the most recent…. but you get the idea i want to downgrade. Thanks for any help!