@ialvi 

This is a limiation of cable products. They are regulated by CTMS and firmware is only available as a push update from the ISP over the cable line.  Manual updates are unfortunately not possible.  You would need to contact your cable ISP and ask them to preform a push update to your gateway.  A note of caution though is sometimes the agent will say they don't do that.  That you would need their branded device for them to do that.  If they say that you have an agent who has not been fully trained or doesn't know what they are talking about.  You would need to request an escalation.  The escalation/manager should know that they are the only ones who can push updates to the router/gateway and be able to assist you.