I’m one of those who always need to have the latest version of everything, regardless of the drawbacks that might lead me. I’m, by definition, an early bird. Having said that, it’s easy to figure out that my Surface RT was running Windows RT 8.1 Preview.
- Go to Windows Update, desktop version, and install all updates (even the optional ones)
- Try a reboot, just in case
- If the Store is still refusing to show the update, open a browser and go to this URI ms-windows-store:WindowsUpgrade
That last URI should open the Store and show the update. Keep in mind that the process will take up to 2 hours and there is no indicator whatsoever about the progress of the update. You can take a look at the Task Manager to see CPU and Network usage to ensure that something is really going on.
Hopefully after that process you’ll have a Windows RT 8.1 RTM device ready to be used