Windows 8 consumer preview -avinstallera??

No. To go back to your previous version of Windows, you'll need to reinstall it from the recovery or installation media that came with your PC; typically DVD media. If 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, you won’t be able to use the recovery partition on your PC to go back to your previous version of Windows.

windows.microsoft.com/en-US/windows-8/faq