This is a test of commonsense. Complete the next sentence:

How to upgrade ubuntu to windows operating system 
Insert the windows installation disc and reboot the system. 
In the boot-up screen, press the key labeled to enter bios, i.e. del, f1 or f10. In the bios, change the boot settings to allow the pc to boot from the optical drive, i.e. cd-rom.
Save the changed bios settings and restart the system. Press the " enter " key to boot from the cd and thereafter press the " f8 " key to accept the terms and conditions to use windows operating system.