There is no manual update can be done for the modem. Even for the device owned by the customers only service providers can send the updates to the modem since they are the one activating and sending signals so only ISP having option to send the updates when its required.

It got me frustrated, both ISP and Arris cannot solve my problem 

I understand your frustration. 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 over distribution by the service providers.