Factory reset using the reset button
There is a factory-reset button located at the back of the modem. To do a factory reset, hold down the reset button with apaper clip and keep an eye on the status Led on the front of the unit. When the status led goes off release the reset button and after about 20 seconds the led will come back on and then you should be able to access the router using the default IP-address (192.168.1.1).
Resetting the product will cause it to loose all the settings so make sure to have ISP documentaion available to you.