Webstore, Windows 8 upgrade paths
You can upgrade to Windows 8 Pro and keep Windows settings, personal files, and applications from the following Windows operating system editions:
What versions of Windows can upgrade to Windows 8 and keep Windows settings, personal files, and applications?
• Windows 7 Starter
• Windows 7 Home Basic
• Windows 7 Home Premium
• Windows 7 Professional
• Windows 7 Ultimate
You can upgrade to Windows 8 Enterprise (Volume License) from the following operating system editions:
• Windows 7 Professional (Volume License)
• Windows 7 Enterprise (Volume License)
• Windows 8 (Volume License)
Upgrade installations from retail versions of Windows to Volume License versions of Windows is not supported. To change from a retail version of Windows to a Volume License version of Windows, you must perform a clean installation.
It is not possible to perform a cross-architecture installation (32-bit to 64-bit) Windows Vista with SP1 or later, (32-bit to 64-bit) Windows 7 or (32-bit to 64-bit) Windows 8.