I’m pretty sure my SBG8300 firmware is up to date.  It is Firmware Version:01.01.137.NCS 

FWIW I just went to Arris.com/support and found the page for this modem, only to find that there listed under “Drivers and Firmware”  the following message:  No Drivers & Firmware Currently Available.
 

:

Thank you for responding, but my Arris firmware Version is 01.02.078.04.NCS and may need to be updated. That website hasn’t helped me locate if there is a new one or not. (Chase)

I was able to connect with tech support in a chat window.  
Try this link and select “Live Chat”

https://arris.my.salesforce-sites.com/consumers/ConsumerProductSupport?t=Chat1

MisterRand, Thank you. The chat is currently closed, but I’m looking forward to going there for an answer. Thank you, again. (Chase)

The firmware is part of the provisioning form the ISP. Nothing the end user can do to update it. Its pushed by the ISP. 

Plemans, Thank you for responding to my question. It sure would be nice to know what the latest version is--just to know how out of date mine could be. Again, thank you. (Chase)

After contacting the chat service, I was advised to contact my ISP. I contacted my ISP and was informed that the responsibility for updates comes from Arris and that my ISP doesn’t have information available about the latest version, etc.

After contacting the chat service, here’s the answer for anyone else who may have the same question or concern: (Chase)

http://arris.force.com/consumers/articles/General_FAQs/Upgrading-Firmware-on-Cable-Modems-Gateways