There are two ways to change the Wi-Fi name and password for the SBG10.
The first option is through the SURFboard Central app. By setting up the app, you can easily change the Wi-Fi name and password.
Please find the link below, where you can follow the steps to set up the SURFboard Central app and update the Wi-Fi name and password.
http://arris.force.com/consumers/articles/General_FAQs/SURFboard-Central-Wi-Fi-Cable-Modem-Setup
http://arris.force.com/consumers/articles/General_FAQs/SURFboard-Central-Changing-the-Wi-Fi-Name-Password
The other option is through the web-based interface (GUI), where you can also change the Wi-Fi name and password.
Since you are locked out of the interface page, please restart the modem and try using the login credentials provided in the link below.
http://arris.force.com/consumers/articles/General_FAQs/SBG10-Web-Manager-Access
After logging in, you will be directed to the basic setup page, where you can change the Wi-Fi name and password directly on the front page.
If needed, for your reference please go to this link for detailed steps on how to update the Wi-Fi credentials.
http://arris.force.com/consumers/articles/General_FAQs/SBG10-Changing-the-Default-Wi-Fi-Name-Password