During the BUILD developer conference on 26th June 2013, Steve Ballmer announced the availability of Microsoft Windows 8.1 Preview and Windows 8.1 RT Preview. If you have Windows 8 PC, you can download an ISO image and install it from there. But if you have a Surface tablet, the process is different.
If you are using Surface RT and want to install Windows 8.1 RT Preview, this post will help you getting started. Make sure that you don’t have any language pack installed.