RECOMMENDED: Click here to fix Windows errors and optimize system performance
if you can install it.
The upgrade path from earlier versions to Windows 8 Developer Preview is as follows:
|Installing Windows Developer Preview|
|Install to :||Windows developer preview with developer tools||Windows developer preview without developer tools|
|Window 7||No clean installation||You can install accounts, Keep files and settings|
|Windows Vista||Install clean only||You can install accounts, Keep files and settings|
|Window XP||Install clean only||You can manage accounts and files|
|Install clean is supported on all versions. You will only get full installation options if the installation is running under Windows.|
Application migration is not allowed with the release of Windows Developer Preview, but other options are available to keep your accounts, files and settings in Windows.
Also note that you cannot uninstall the Windows Developer Preview.
To reinstall your old operating system, you must restore or use the installation media.
Here you can find Windows 8.1 & Windows 8 RTM Upgrade Paths.