NEED HELP DOWNGRADING FROM 5.51fw

[biffmaster5000]

ok so i bought my first psp not too long ago used from gamestop with a 1gig stick to go with and a few games....little did i know at the time how much modding and hacking there is on the psp i was use to hacking/modding the xbox360 so im not a noob at soldering and installing firmware! but stupidly before i found out so much i could do with my psp i upgraded so i could connect to the internet at my house(why not right?!) yeah so im a 5.51fw and have no clue how to downgrade so i can get either chickHEN or some other home brew program to run ripped games movies etc.! can someone direct me in the right direction to downgrade this thing i want free shit lol!!! ohhh yeah i have a psp slim 2000