If you are still running Windows 7 or 8.1, you will have about two months to upgrade your OS to Windows 10 free of charge. In July 2015, Microsoft announced that eligible Windows 7 and 8.1 users can upgrade to Windows 10 for free, and this offer will end July 29th, 2016. After the expiration of the offer, if you want to upgrade to Windows 10, you will have to buy a license which costs $119 for the Home edition and $199 for the Pro edition. This free offer is too good to pass, so I strongly recommend you to upgrade your device (PC or mobile) to Windows 10 sooner than later.
If you need a step-by-step upgrade instruction, please read my previous post http://126.96.36.199/2015/07/30/installing-windows-10-using-media-creation-tool-for-free/
To know more about Microsoft’s free Windows 10 upgrade, visit https://www.microsoft.com/en-us/windows/windows-10-upgrade
Enjoy the new Windows 10!