Microsoft has done an interesting thing with Windows 10. Besides providing it as a free upgrade to anyone with an activated Windows 7 or Windows 8 PC operating system (OS) is also one big shareware.
If you want to Activate windows 10 after installation, you need a digital license or a product key. If you are ready to activate windows 10. You can follow these steps.
1. You can select open Activation in setting on your device.
2. Click change product key to enter Windows 10 product key.
3. If your Windows 10 was previously activated on your device, your copy of windows 10 should be activated automatically.
Learn more about Installation errors in Windows 10