If you can't upgrade due to compatibility problems, then I recommend removing the driver. Go to Device Manager (Windows key +R > Run > devmgmt.msc). Locate the driver in the list and then right click it. Uninstall it without rebooting and then launch the installation procedure and it should work. After you install Windows, use the Bluetooth driver to install it. Ignore the errors saying the driver isn't signed for Windows 10.