I’m having the exact same issues. Can’t figure out how to update it or download the latest firmware. Not getting anywhere. May just have to replace it, which is frustrating, because my Arris G36 is not even 2 years old. I hope you have better luck.

It’s been around a year for me, fed up with Arris. Not even able to contact support, the worst decision I ever took to buy Arris.

Researching on new cable modems to buy

If you are experiencing with intermittent internet connection, could you let us know whether the issue is with wired or wireless connection.

If you are having issues with both wired and wireless connection, I suggest you to check the cable signal levels to make sure all are in range.

http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Cable-Signal-Levels

If you are experiencing only with wireless connection, I suggest you to change the Wi-Fi channels and monitor it for next 24hours of time.

http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Changing-the-Wi-Fi-Channel