Microsoft is rolling out Windows 8.1 gradually across their user base.
We have gotten complaints that some users are unable to see the update yet and the ISO files will be available tomorrow…
The Preview release will be open to all users sometime today or tomorrow, but so far Microsoft has only enabled downloads for users of Windows 8 — though we haven’t been able to see the update on every computer that we tested it on.
Those users can begin getting the update by visiting Microsoft’s website and initiating a small update for Windows itself. Afterward, the device will restart and direct users to the Windows Store where an update to the 8.1 Preview release is available to download.
Microsoft says that the full release should be open to everyone sometime soon.