*NEWBIE*questions on downgradeing 4.11 to 3.55

hey guys im new to this site and fairly new to ps3 modding/hacking, the main reason im on here is because i want to downgrade my firmware so i can back up games or get some off the net:biggrin: but i was wondering do i need to buy some hardware to downgrade or can i download the stuff to my external hard drive to do it?

PS3 Slim
Model: CECH-2001A
180GB
Firmware: 4.11

any help is greatly appriciated!:)