Windows 8.1 product guide and FAQ pages are now live. You can download the product guide here. To download Windows 8.1, go to Windows 8.1 Preview page on Windows.com. The Windows 8.1 Preview will be installed through the Windows Store. Please see the Windows 8.1 Preview FAQ for the minimum requirements needed to install the Windows 8.1 Preview.
Microsoft notes that, If you are on Windows RT and have installed a language pack, please don’t install the Windows RT 8.1 Preview at this time. A fix is coming so check back soon.