cannot update R6250 router

I have received several update alerts but kept entering the wrong password. I let it go. The WiFi has gotten very erratic so I tried to get back in after finding the correct password but was sent to the security questions. The first question was correct but the second question wanted my youngest brother's first name, but I don't have a brother and did not select that question. I typed in the answer to the 2nd security question that I had written down and saved but that was not accepted. So I'm stuck.

The router is not very old and is not behaving well and probably needs the updates. I've had the cable company out twice over this issue and last week they swapped out the modem, so I'd like to try the updates before I replace the router.

Any help is appreciated.

Mark