Reinstalling Windows 8

I have an Alienware M17x R4 w/3D bundle, and now an Alienware 17 w/3D bundle.
I want to sell the M17x, but first want to wipe everything and reinstall windows. It didn't come with any disk for that, but my 17 came with an operating system disk. I have the office disk for both laptops though.
My question is, can anyone help me out and tell me how I go about resetting my laptop completely?
Thanks in advance :)