Not enough info available to help.
What firmware you on currently?
What do you want to be able to do?
Offline or online ?
If you want help provide details.
Alot of options depending on what you want to do.
Honestly you probably need to do some research as there is a ton you don't know.
If you are looking for a 4.31 CFW to install on your OFW PS3, then, you can't.
If you already have a PS3 with FW 3.55, then just install one of them, there are a bunch. I can personally recommend rebug firmware.