Create a Bootcamp partition with Bootcamp assistant and install Windows 8 from scratch.
More tedious and not exactly fool-proof: If you want to copy your current Windows 8 installation to Bootcamp you might use the backup and restore functionality in Windows 8 to backup it under Parallels and restore that backup under the Bootcamp installation, at this point if everything is working you might go back to Parallels and add a new VM with the bootcamp partiton, finally you can discard the old VM.
There are other methods like using cloning software, but requires knowledge and experience (the problem with Windows is migrating to what is to Windows different hardware, even if it's the same machine, a virtual machine appears as completely different hardware from native).
Like I said in my initial post, although it is easy to go one direction, from Bootcamp to Parallels, it doesn't work the other way around, you have to get a little creative. And please don't ask for step-by-step instructions, personally, I'm not very willing as it's very tedious and requires quite a lot of time to make them fool-proof, there are somem possible road blocks with doing such migration that have to be dealt as they come, and predicting them all is quite hard work.
Last edited: Mar 17, 2013