You're, inevitably, going to get a boilerplate answer from Arris saying that it has to be done from the ISP. They'll give you a cutesy answer that because of the DOCSIS standard and this and that that they can't give you an update. 

Rest assured, you do own your modem and you should have the power to update it yourself, but this looks to be another way for corporate interests to control the masses and their buying habits whilst controlling information flow.

I won't go into the weeds on the subject, but this really smells like a class-action lawsuit brewing. 

Firmware updates are like automatic process. ARRIS develops the software update and makes it available to service providers.  The service providers qualify, test, and distribute the software update to devices on their network.  ARRIS has limited control or visibility on distribution by the service providers.

Thank you both for your responses.  I will call the ISP and see what they have to say about this.  

Their sales dept. is pushing for me to get a new package from them which comes with fiber optics, which I don't have. I would then need to rent a modem router combo from them, which I stopped doing when I bought this one.  So I own my own modem, and have a mesh network for different floors in my house. So their new deal is that rental is free for one year, but then you are up for plan renewal and you know how that goes..…

I can't get fiber optics from them without renting a combo modem router.

I don't think I want to upgrade now, and so I was wondering what happens with software updates. 

Thank you for the response.

It would be nice if when you advertise a modem as DOCSIS 3.1 the DEFAULT software/firmware on it showed DOCSIS 3.1 and NOT DOCSIS 3.0.  I wonder how many modems are out there like this. When I factory reset my SB8200 it showed docsis 3.0.  The second one I bought for a relative had not even seen a ISP coax connection and it said the same thing------docsis 3.0…. Now all the sudden certain ISP’s are saying “we don’t update THAT” when they clearly have for years. And why would the ISP have to qualify and test the updates, ARRIS is the one who manufactured the modem and software in the first place. Aren’t you more qualified to supply us with a modem update than the ISP?   

If your modem has green led light on the front panel that indicates 3.0 DOCSIS. Blue color - Indicates DOCSIS 3.1 operation (high-speed Internet access) which may not be available in all locations.  Check with your service provider for availability in your area. 

Regarding firmware update, ARRIS develops the software update and makes it available to service providers.  The service providers qualify, test, and distribute the software update to devices on their network.  ARRIS has limited control or visibility on distribution by the service providers.

  Well a family member just got an Arris SB8200 (DOCSIS 3.1) I put it on their gigblast and the modem was saying DOCSIS 3.0 still. And no blue LED .So I opened the other new box, I was saving until they forced me to upgrade, and the admin page also said DOCSIS 3.0.(never online)  That is NUTS, I didn't buy a modem to upgrade just for it to have DOCSIS 3.0 let alone it says it is a HW.VER.3 when everything else I see out there says ver 6-7. 
But to rely on ISP for something I thought I bought already, I feel scammed.Or is it in some small print behind the big bold DOCSIS 3.1 package advertisment... I'm well aware I won't get 1-2gig speeds if I am not paying for that package.    What do you classify as “high-speed Internet access”?