Microsoft has just announced that Windows 8.1 is available as a free download in the Windows Store, so all Windows 8 adopters can get it right away.
As expected, Windows 8.1 is offered free of charge to those running Windows 8, while those whose computers are still powered by an earlier version of Windows need to wait until tomorrow.
Boxed copies of Windows 8.1 will go live tomorrow and will be available from $119.99 (€90) for the basic version and $199.99 (€150) for the Professional version.
Keep in mind that in case you are running the Preview build of Windows 8.1, upgrading to 8.1 RTM will remove all installed apps and settings. Moving from Windows 8 to 8.1, on the other hand, saves all your files, with the download taking care of everything.
Update: if the update doesn't show up, here a few instructions to download Windows 8.1.