Unfortunately, Win 8.1 is also much harder to undo than other operating-system updates. Contrary to what its "point release" number might suggest, 8.1 is not some minor update you can roll back through the Windows Update control panel. And it's more difficult to roll back through the other usual mechanism in Windows, a system-recovery process.
If you decide that you want to install Windows 8.1 Preview using the ISO, you won't be able to uninstall it. If you decide to go back to your previous operating system, you'll need to reinstall it using the recovery or installation media that came with your PC, which is typically DVD media. If you're running Windows 8 and you don't have recovery media, you might be able to create a USB recovery drive. If you're running Windows 7, Windows Vista, or Windows XP and you don’t have recovery media, you might be able to create it from a recovery partition on your PC using software provided by your PC manufacturer. Check the support section of your PC manufacturer’s website for more information. After you install Windows 8.1 Preview, you won’t be able to use the recovery partition on your PC to go back to your previous version of Windows.