WinKey was a useful tool that is no longer supported.
Disclaimer: it seems that the publisher's website is closed and that the software is no longer supported. Thus, it may no longer work on your computer, or run with recurring error messages.
In order to install or uninstall Windows, you need a registration key. WinKey is a tool that helps you to get a serial number. You have to run the software before formatting the OS.
You can download and use this tool for free.