1. You need to go to Microsoft upgrade page: Windows Upgrade Offer - Landing Page
2. Select your country from the list — over 140 countries can avail this discount. Hit the Continue button. The exact cost of Windows 8, depending on the country selected, will be shown.
3. Register by entering your personal information, PC model, brand, date of Windows 7 purchase, and other information. You will know if you are eligible or not on this steps.
The last day to register and order your Windows 8 Pro copy at this price is 28 February 2013. Microsoft is offering Windows 8 at a dirt cheap price (available for $30 at Microsoft’s online store) limited only for a couple of months, then the price will shoot up to $169 in January 2013.
If this type of thread is not allowed here, please delete it (to WF mods). I'm just trying to help.