If you’re already using Windows 8, getting 8.1 is sort of a no-brainer. Although the improvements aren’t mind-blowingly spectacular, many of them are useful, such as customizing the split screen between multiple apps, better multi-monitor support, a more configurable start screen, and a lock screen that acts as a slideshow. Windows 8.1 allows you to boot straight to the desktop. It also brings back the Start button, but that doesn’t really work the same as the real start menu in Windows 7 and before, so you’re better off still using a Windows 8 start menu replacement.
Current Windows 8 users: Head over to the Windows.com page for the link to the free download on Windows Store (or just head to the Windows Store on your computer). When you update, your files, desktop apps, and settings will be transferred–and you can even keep working while the update is happening. (Download can take anywhere between 30 minutes to several hours, according to Microsoft.)
Be warned though this can take quite some time to complete. It does appear to have been well tested and the updates that I’ve been through have happened gone very smoothly.
You can get it from the Market Place – it should turn up as the prominent tile on the left