From the page: "Reboot:
1) Turn on iPhone.
2) Hold Sleep/Wake button (top right) until a red slider appears and says Slide to Power Off.
3) Slide the red slider.
4) Once the chasing lines are gone and the screen is black, hold the Sleep/Wake button for about 2 seconds. Your iPhone is now rebooting.
1) Power iPhone on.
2) Hold the Home and Sleep/Wake buttons for about 7 seconds, or until the screen turns black.
3) Your iPhone should reboot. If it doesn't don't worry, just hold the Sleep/Wake button for about 2 seconds.
1) Connect to iTunes.
2) Allow your iPhone to back up and finish the sync.
3) In the Summary tab, click the Restore button.
4) Click Restore and Update to the confirmation message that appears.
5) Follow on-screen instructions from there on.