Download the
media creation tool and follow the steps. If you're in India it should have been up by now as it was available on the day of release through the windows update itself, I got it through WU but had some issues like it was stuck on preparing for installation. Henceforth, I updated using the tool and it was rather a quick and simple process than upgrading through windows update.[DOUBLEPOST=1438421666][/DOUBLEPOST]
There will be a skip option beneath it somewhere when it asks for the product key during the installation of Windows 10, that'll just scan your PC for the product key and proceed ahead if you own a legit copy of Windows 7/8.