it is possible to move to any firmware via recovery.
just move the "RECOVERY" folder inside the "files for recovery" folder to the GAME folder
get update eboot (any)
rename it to UPDATE.PBP (if that doesn't work, rename it to UPDATE)
put that into the "RECOVERY" folder
turn PSP off (if it was turned on), then hold R and turn psp on
select run program at /PSP/GAME/RECOVERY/EBOOT.PBP and press X
press X again when disclaimer comes up and your psp will begin degrading (or upgrading if you used 2.80/2.81 update ebbot)