The process is quite easy, but before doing so, you should make sure you're already on the most recent Rogero CFW.
Originally Posted by steverobbo
To upgrade HDD:
Download the most recent Rogero CFW (Rogero 4.40 v3) and rename the file to UPDAT.PUP
Put the file on your usb stick in the following file structure "root/PS3/UPDATE/UPDAT.PUP".
Turn of ps3
Plug USB Stick into your usb on ps3
Put in the new hdd
Follow the on screen instructions (It should ask you to format the hdd, then it will have you reinstall the cfw, etc).
All in all it's just another brick in the wall.