Step 1. Be willing to face some trials and problems and don't give up easily.
Step 2. Download a working copy of windows 8.
Step 3. After that you need to put this into either an external hard drive or bootable USB.
Step 4. Make the USB or External drive a bootable drive.
And when you tell me where you will put your windows 8, we will further continue our lessons.
In the unlikely case, you are booting from a DVD of windows 8, and you have it physically, you're in luck.
All you need to do is
Step 1. Go to BIOS
Step 2. Open BIOS Settings and go to Boot Devices
Step 3. Change 1st boot device to Cd/DVD Drive.
Step 4. Save changes and exit.
Step 5. The computer will restart and will say press any key to boot from cd...
Step 6. Press a key.
Step 7. Windows 8 setup will start loading.
Step 8. Follow instructions after that.