Yesterday Microsoft released a Preview version of the next Windows, Windows 8.1 Preview. It will be a free update for Windows 8 consumers later this year through the Windows Store, but from yesterday people can take a first-hand look at many of the new features and improvements themselves.
Before you install the Windows 8.1 Preview, it is also highly recommended you backup any files you have on your PC or tablet first. Please see the Windows 8.1 Preview FAQ before installing, which includes information on how to go back to Windows 8 if you need to. There are certain cases in which you will not be able to go back to Windows 8 after installing the Windows 8.1 Preview so please read the FAQ before proceeding.
For details on the installation process, please refer to this post.