In this case we don't have option on the modem interface to reset the login credentials so to access modem interface using default login credentials you need to perform hard reset on the modem. But after resetting the modem will go to default setup any custom settings will be removed so use the default network name and password to connect to your network. Please follow the steps mentioned on the article below to reset modem.

           http://arris.force.com/consumers/articles/General_FAQs/SBG7600AC2-Factory-Reset

Thank you...the reset worked and I will stick with the default setup since I don’t have a clue on how to make that setup any better!