Windows 8 Is it possible to upgrade to Windows 8.1 final from RTM?

The short of it....NO. Unless you have a 8.1 product key...the only way is to upgrade through the store.
 
Sure....
Most of us with either TechNet or MSDN subscriptions have been running Windows 8.1 RTM for a while now and today all you need to do is open control panel and run Windows Updates and that should bring your installation current with today's General Availability Release.