For non-Windows 8 devices, here is how upgrading to Windows 8.1 using the retail DVD and download software will work:
Windows 7: Consumers can upgrade a Windows 7 PC which will bring along all their files, but will require them to reinstall desktop apps including Microsoft Office.
Windows XP & Windows Vista: Windows 8.1 is not designed for installation on devices running Windows XP
or Windows Vista. Although not designed or recommended for devices running Windows XP or Windows Vista, consumers still wanting to upgrade from Windows XP or Windows Vista should buy the retail DVD instead of using the download and boot from the DVD to do a clean install of Windows 8.1. Note: files, settings and programs will not transfer – Consumers will need to back up their files and settings, perform clean installation, and then reinstall their files, settings and programs.