I have tried to upgrade the windows 10 from windows 7.
It said it is free.
One of the worst type of upgrade provided by windows.
If you get power cut or some crash happened while upgrade, it will restart and says you don't have valid key.
Then headache started. So Please keep shut and use the old windows OS itself.
Windows always proves itself every-time, it is one of the stupid in upgrading.
Bye BYE windows