Microsoft, under the offer which is set to expire tomorrow, sends out emails to qualified buyers containing a code. This code is then used by users to download a discounted copy of Windows 8 Pro from Microsoft’s official website.
In order to take advantage of the offer, you must ask for the discount before the deadline and also pay the $14.99 towards the upgrade offer and then download the upgrade. The same deadline applies to all those who registered earlier for the upgrade discount, received the discount code in their email, but haven’t downloaded their copy of the Windows 8 Pro.
The Friday deadline doesn’t force you to actually install the Windows 8 Pro upgrade on your computer. You have to ensure that you download your copy and create for example a bootable DVD for later installation.