a quick google search found this :

Turn your router upside down or look on the rear for a small pinhole. It should be labeled "RESET." With the router turned on, unbend a paperclip and insert it into the hole. You will feel a small button inside, which you'll want to press with the tip of the clip. Hold the button down for 10 seconds, or until the lights on the front of the router stop blinking. The router will reboot within about a minute and be ready for configuring from its virgin state.

let us know how you get on