All the Windows XP and Vista users who skipped Windows 8 won't be able to upgrade to Windows 8.1 directly. "Windows 8.1 Preview upgrade installations from Windows Vista and Windows XP aren’t supported," Microsoft mentioned on its website. The only way to install Windows 8.1 is to first buy Windows 8 licence, upgrade from XP or Vista to Windows 8 and then upgrade to Windows 8.1 from the Windows Store. 