It will ask your for the Windows Version you want again, and will ask for Windows Key if you have one (you don't need one to Install Windows, but it will be the unregistered version, meaning you wont be able to customize a few things regarding appearance, but its a fully functioning version of Windows 10!). Once you select your desired Windows. Windows 10 never stopped being free upgrade, just use the media creation tool to upgrade from 7, and once license is activated, you can link it to your MS account also, then you can then use the media creation tool to create a bootable USB to clean install with. Even a non activated windows 10 is free to use, if you don't mind the watermark.
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