For a start, there’s actually two distinct offers on the tablet for those looking to jump on the Windows 8 bandwagon: One where you can upgrade your current computer OS to Windows 8 Pro for £50 (from Windows XP to Windows 7 including Starter Edition) regardless of the purchase date.
The other is where you can buy a £15 Windows 8 Pro upgrade for a personal computer (desktop, tablet, laptop) with Windows 7 excluding Starter Edition purchased between 2 June 2012 and 31 January 2013.
You will be able to buy the installation media for an additional fee. By default, you will be offered a downloadable option to upgrade your current OS. Also, the upgrade itself is not tied to any PC in particular, which means that you can download one copy and install it on several computers provided that they all come with Windows 7 installed.
Surprisingly enough, the upgrade version offered is Windows 8 Professional (arguably the best non-entreprise version) rather than Windows 8 vanilla. Note though that Windows Media Center is available as a paid-for option only and is not included in the OS.
The last date to redeem the promotion codes for Windows Upgrade Offer, download and install Windows 8 is the 28 February 2013.