Microsoft indeed made the Windows 8.1 update available for all users, but some users still can’t download it right now, as Redmond continues the global rollout.
But in case you’re not seeing the update in the Windows Store right now, here’s a small trick, courtesy of WindowsObserver.
Go over to this page, which provides information regarding the updating from Windows 8.1 Preview to Windows 8.1, click on “I installed the preview from the Windows Store or I installed the preview using media while Windows 8 was running” in the “Updating to Windows 8.1 or Windows RT 8.1” section and then hit the “from the Windows Store” link in the expanded text.
The link should then launch the Windows Store and bring up the Windows 8.1 update, regardless of whether you are trying this on a Windows RT or a desktop computer running Windows 8.
Please note that servers are a little busy right now, so the whole process could be a bit slow at this point.
Update: according to some reports, installing the latest patches via Windows Update could fix all problems. Additionally, a number of users are reporting that the 8.1 update cannot be installed on machines running the Enterprise version of the operating system.