[WindowsCentral.com]

Windows 10 includes many ways to help you change your product key, and in this guide, we'll show you five of them.

Windows 10 requires activation to verify you're running a genuine copy; a unique product key is used to ensure the a single licensed copy of Windows isn't being used on more than are allowed.
Occasionally, you may have to change the product key. If you're getting Windows 10 for the first time and a product key wasn't provided during the installation, or a generic key was used to upgrade, you'll need a new valid product key to activate the operating system.

Full story from the WindowsCentral blog...