You need a homebrew compatible firmware to go to custom FW. (1.50).
I am not upto date with the new ways, but ive heard Pandoras battery can be used to downgrade.
Search the forum about downgrading with pandora battery.
It will take you a while and you need to research first. (just to warn you).
(btw, this goes in the Psp help section, just so you know were to put your next psp querry.
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