If you want to login modem interface using default login credentials you can perform hard reset on the modem since there is no option to reset the modem login credentials alone 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.

http://arris.force.com/consumers/articles/General_FAQs/SBG7600AC2-Web-Manager-Access

After resetting connect device to the modem default WIFI network then try accessing modem interface using default login credentials by following the steps mentioned above.

Tried hard reset and it took me back to requiring my ID and password which I do not have. Once in the hard reset the obvious is that I can’t use my computer. It said something about my password in key something i cloud. I don’t know where to find this. Can you guide me to where my password might be saved. It said it was saved at that location.

After factory reset the modem, to login the GUI web portal use username as admin and password as password.

http://arris.force.com/consumers/articles/General_FAQs/SBG7600AC2-Web-Manager-Access

And if you are looking for Wi-Fi password, please check the default password at the bottom of the modem.