Are you trying to build a linux ubuntu machine? If so, you have to take that data, and convert it to an ISO (bootable) disk. "ISO 9660 is a standard published by the International Organization for Standardization (ISO), defines a file system for CD-ROM media."
Then once you have converted it to an ISO, you need to get into BIOS. Your PC make and model is dependant on what button to push to get into BIOS. Or, put the disk in and see if it prompt to boot from disk. You will more than likely have to get into BIOS and tell your machine to boot from CD-ROM!
Then after reboot, you should see a prompt that says HIT F2 to boot from disk, press F2.
Once you spin that disk, your other OS will go away (if you don't have your disks partitioned correctly)!