N600 WiFi Cable Modem router Model C3700 will not connect.

I have comcast and didn't rent the xfinity modem router, so I purchased my own. I originally bought this product and Comcast support told me the router was bad and to get a new one. I returned the first, only to be stuck with the same issue.

My issue is as followed:
I cannot connect to the internet. I have logged onto my router and it continues to say "cable connection 'in progress'".
So far from what I have found on the internet is that I might need to update the firmware. Unfortunately, I don't know how to do so.

Please help!