Windows 10 was a free upgrade to the users of Windows 7 and Windows 8.1 Unfortunately due to the way activation worked, a clean install was not possible and you had to upgrade using their upgrade tool. When used this way Microsoft ascertained if your copy was genuine and tied your hardware to a Windows 10 activation, very similar to the 8 to 8.1 process. This made a lot of users angry, including me as a clean install was an issue. So now Microsoft has allowed all Windows 7 and 8.1 keys to be used as Activation keys for your Windows 10. Just go to Settings and Activation and enter your 7/8.1 key to activate your Windows 10. This allows for easy and clean installs. From microsoft:- Tweakbytes tip:- Well if at any time the activation fails, just disconnect from the net and allow the phone activation screen to come up. Then just call up Microsoft and go ahead with your activation. If it still fails the IVRS will transfer your call to a support executive. Just explain your issue and they will give you the code. Microsoft activation team is quite helpful. Please call the correct regions though. Do not use Skype and call the US/UK tollfree numbers, use your own local numbers. For the users wondering if they should upgrade, we say there is nothing as such significant in Windows 10 you cant live without. Those who like cutting edge surely can upgrade. Before upgrading wait for a few more builds and patches to come out, about 1-2 months or so and then go for it.