Upgrade version means you have to install Windows7 from with in a Genuine Activated Windows Operating System. NO FRESH INSTALL.
Full Version can be installed on any computer that meets the basic requirements.
You do not need any operating system pre-installed.
Either Full Version or OEM (Builders) Edition is the prefered way to install any OS.
The Full Version provides support from Microsoft if you need it. The OEM Version is considerably less cost and there is NO Support from Microsoft.