to update to the latest cfw you'll need:
1.to download the one of your choice, for example for the latest rebug cfw head over to http://rebug.me
and grab the most recent one.
2.have a USB stick formated to fat32
3.create a folder inside the USB called "PS3" and inside this one another folder "UPDATE" the folders names must be in caps.
4.when you finish downloading the cfw rename it to "PS3UPDAT.PUP".
5.now in your ps3 go to "system update" then choose "update via storage media"
NOTE: disable any internet connection from ps3 and remove any game disc from the console, make sure no game is mounted also.