That's great and all, but even from Microsofts site that you just linked:
In order to upgrade to Windows 10 using the ISO image or upgrade media you created using the media creation tool, you need to select the Upgrade this PC now option.
If you performed a clean installation instead of an upgrade, you'll be asked to enter a Windows 10 product key or buy a new license in order to activate Windows 10. This is because we weren't able to register your free upgrade entitlement with the activation servers because you didn't upgrade to Windows 10. To fix this, you'll need to go back to your previous version of Windows, make sure the previous version is activated, and then upgrade to Windows 10."
I don't have a previous version of Windows, all these guides assume you came from a previous version, rather than fresh install. There's also no where to 'buy a license key' because the entire point of this is to get rid of them. Is there a location to buy a legit key?