Slim / 4.46 OFW --> CFW

Hey,

i wanted to ask particular what i have to do, if want to install a CFW (Rebug?) on my PS3 Slim.
Its a CHECH-2004A with 4.46 OFW and the MinVerChk says "Update data of version 2.70 or later can be Installed on this system". Sorry for asking so stupid, but i dont want to do something stupid, what i cant redone.

Thanks in advance and sorry for the bad english
Greetings