Instructions
Select the "Settings" heading in the PS3 menu and select the "System Update" subheading.
Select "Update via Internet" on the next screen. The PS3 connects to the Sony update server and checks to see if there are any software updates available. As you are on CFW, you are always given the opportunity to return to Sony firmware.
Select the "Download" option when the results are returned from update search. The PS3 downloads the software update directly to the PS3 hard drive.
Select the "Accept" option when the download completes. This gives Sony the notification that you agree to the terms and risks of the software update.
Press the "X" button to update the PS3 software, getting rid of the jailbroken CFW on the PS3 and replacing it with official Sony firmware. The PS3 will reboot during the procedure.