Microsoft has removed Windows RT 8.1 update from Windows Store temporarily. There seems to be some issues affecting users while they updating their devices. Microsoft is aware of the issue and already investigating it.
Microsoft is investigating a situation affecting a limited number of users updating their Windows RT devices to Windows RT 8.1,”
“As a result, we have temporarily removed the Windows RT 8.1 update from the Windows Store. We are working to resolve the situation as quickly as possible and apologize for any inconvenience. We will provide updates as they become available.”
Expect the update back in store soon! I myself updated my Surface RT and the update process for smooth and now, I’m enjoying the Windows 8.1.