Yeah, obviously you can, that’s what you have paid for. Follow these steps:

• Open settings, you will get a link sort of option as the bottommost line.

• After that, click on ‘Go to store’ option present there.

• After going to store, you will get to see a page which asks you to buy Windows but has a small link allowing you to enter your product key.

• Now, Windows will ask you for permission to allow Windows Activation service present in PC to activate the Windows. Windows does not allow to take screenshot of that permission window or maybe I’m not aware of the correct method to capture that.
• Now a small window will appear asking you to enter your product key.

• Enter the key and activate your Windows.

Thanks, Hope it helped

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