How do I update my old Xfinity Home Security touchscreen to a new WiFi name and password?

I have an old Home Security touchscreen, showing model TCA203COMG on the underside. I recently updated my Xfinity internet Gateway so I have a new WiFi network name and password. I cannot find a menu option on the touchscreen to change WiFi, and also cannot find a way to do it on the Xfinity home app on my smartphone. I tried restarting the touchscreen from the Home app, but it is not doing anything to the touchscreen - I suspect it’s because I don’t have a WiFi connection between my smartphone and the touchscreen. 

Two questions:

1. How do I reconnect my touchscreen to the new WiFi?

2. Is it time for me to replace the touchscreen with the newest model?

TIA