Last June, during its Build developer conference, Microsoft released a free public preview of Windows 8.1. The final release of Windows 8.1 and Windows RT 8.1 arrived on October 17, and is a free upgrade to existing Windows 8 and Windows RT users.
If you’re still running the preview, take note that it’ll expire today, January 15. If you’ve not fired up your machine for a while, you should now see a notice advising you to upgrade every time you sign in. After January 15, your PC will also restart every 2 hours, and you’ll lose any unsaved data.
Of course, if you’ve Windows 8, our recommendation is to do the upgrade - it’s free after all. The download can be done through the Windows Store app. All your apps (both desktop and Windows Store apps) need to be reinstalled, but your personal files are preserved. For those who want to know how to go back to the OS that was on the machine prior to installing the preview, Microsoft has the details, so feel free to hit the source link below.