Update: Windows 8.1 Preview has been released! 
Windows 8.1 is a free update for Windows 8 consumers with tons of new features and enhancements. You can download it through Windows Store or download the standalone ISO that would allow you to set up a dual-boot configuration and install the operating system on a different partition.
Downlaod: Windows8-RT-KB2849636-x64.msu and install it through Windows Store.
Downlaod: ISO file for clean installation or dual booting