You need to know there are plenty of web pages on this but often you find out that you don't have the right OS to do this properly. That is you need to install 7 first, leaving open space for 8 later. Many folk don't have the right Windows 8 OS. That is, the PC came with 8.
I bought a pc with win 8. I want to add win 7 from a disc. How do I do this?