you need to know what PS3 you have, if it can be jailbroken and what FW you are on.
Run minvercheck on your PS3 as if it were an update (link in my sig below) to confirm if your PS3 can go down to 3.55 or below, and look on the back of your PS3 for the CECH-xxxxx serial.
settings>system settings>system info for FW version
You need to be on 3.55 OFW inorder to jailbreak. There is no USB/software method to downgrade, and you cannot software jailbreak any firmware HIGHER than 3.55.
you can downgrade SLIM 210xk machines using hardware flashers, but you wouldnt need to solder if you used a E3 NOR clip.