Windows 8.1—a free update to Windows 8—is coming later this year, and a prerelease version is available now for you to try. Windows 8.1 has new ways for you to personalize your PC and includes a wave of awesome new apps and services. This preview is mainly for experienced PC users, so if you’re not sure whether it’s right for you, read the FAQ.
What’s New in Windows 8.1?
The Windows Team provided a great detailed list of the new features on the Windows Blog