Before we go ahead, remember, after you install Windows 8, you won't be able to use the recovery partition on your PC to go back to your previous version of Windows. Once you've decided to take the dive, download the Windows 8 Release Preview Setup from here.
The setup will check if your PC can run Windows 8 Release Preview and provide a compatibility report that you can save or print. Make sure your devices are connected to your PC and turned on before you run Setup.
The Setup program will automatically select the optimized version of the download according to the architecture of your PC (32-bit or 64-bit).