C6250

In the last 60 days, my router/modem will not stay connected. I loose internet mutliple times a day. Thinking it was a Service Issue, I had Spectrum come out TWICE and all is fine on their end. They think there is something wrong with my router/modem device.  When I log in, it says my firmware is up to date but even still, there is no where that allows me to update it. I am not sure what to do or try. I have done multiple factory resets as well.  It's less than 3 yrs old and just randomly started happening.  I also downloaded the Nighthawk App and it says the firmware IS out of date but there is no way to update. I am lost. Can anyone suggest something else to try??