Microsoft can't say it, but most carrier branded phones (Verizon, AT&T, etc) won't update using the Upgrade Advisor. All you get is that there is an update available but waiting on your carrier to approve it. Instead the only way to upgrade to W10M in this case is to use the Insider app,

Your request appears to be from an automated process

Once upgraded that way then it is just a matter of deciding whether you want the current release build (Threshold) or preview build (Redstone).