Caution:
Once you click Next,
the installation program begins writing the operating system to the
hard drive(s). This process cannot be undone. If you have decided not to
continue with this installation, this is the last point at which you can
abort the installation process.
To abort this upgrade, press your computer's
Reset
button or reset using Control-Alt-Delete, and then remove the installation media between the
unmounting and reboot screen messages.