Note: if you have not done so, please read the introduction to Upgrading a PS3 Hard Drive before performing these steps.
Once you have formatted the new hard drive using PS3's system software you are ready to move any content that you backed up in an earlier step back to the PS3 console. Just hook the USB hard drive back up to the PS3 and move the content you copied earlier.
You're done! Congratulations, you just upgraded your PS3 hard drive. I recommend keeping the original PS3 hard drive in a safe place, in the event anything goes wrong with your PS3 I do not know how their support team will react to an upgraded hard drive, so you'll be able to swap it to the factory original before sending it in for repair, etc.