What you want to do is called dual booting and you will be best served by following
this guide.
On the flip side, you will need drivers for your installation of Windows 7. Is the notebook you own an
Asus X553MA or another model number? If not then please state your model number so we can source drivers that are necessary for your unit.
* The
Asus F553MA looks strikingly similar to the X553MA though as they both exhibit the same specs, aesthetics and minimum support of Windows 8.1
I do see one possible barrier to moving with a dual with Windows 7 on the other partition and that is no driver support. Perhaps if yu could manually hunt for the drivers as per your hardware specs.