How do I completely uninstall Windows?

In System Configuration, go to the Boot tab, and check whether the Windows that you want to keep is set as default. To do that, select it and then press “Set as default.” Next, select the Windows that you want to uninstall, click Delete, and then Apply or OK.

How do I uninstall Windows 8 and install Windows 7?

Once into the Boot Options menu, you will first find “Secure Boot” and disable it. Still in the Boot Options menu, find “Legacy Boot” and change it to enabled. You will now be able to boot into your Windows 7 installation media.