Do not know your particular model, but generally you have to change the boot order in the bios to boot from CD.
Access to the bios hitting F2 (or ESC in some model) at the startup screen, go to the boot-menu of the bios and move your CD device to a priority higher than the hard-disk, save the changes and reboot... voilà. If your laptop does not have a CD-DVD probably can boot from some type of external usb-device (CD , HD or flash-disk), the process will be the same.
Most laptop hitting F12 key at startup screen give you directly a menu to choose the boot device.
Hope this help