Update on 30th July 2015: Microsoft Windows 10 released globally and the Free Windows 10 Upgrade is now available for 190 countries. In its recent blog post microsoft have mentioned the eligibility details other instructions for Windows 10 free upgrade. If you want to buy a new Windows 10 License key, then do visit Microsoft Store for Online purchase.
Microsoft has announced the release date of Windows 10 today, which is July 29th, 2015. They also updated their official Microsoft Windows 10 page with details to Upgrade to Windows 10 for Free. Microsoft already rolled out ad based popups for existing Windows 7 and Windows 8 users with steps to upgrade to Windows 10 for Free.
If you haven’t received any such notification or pop up in your Windows PC which has genuine license, you can reserve Windows 10 upgrade offer by visiting the official page from the above link.
Microsoft has released the Beta version of Windows 10 by the end of 2014, and so far the progress is amazing. People who have downloaded and registered for beta started to like Windows 10 advancements with every beta released so far.