Un-installing and Re-installing

Hi guys!
About 6 months ago I built my first rig. Recently I've gotten an ssd and I want to install my os on it, how do I wipe windows from my hard drive and then re install it onto my ssd? Although I have a external drive I can use to transfer all the stuff I have on my hard drive at the moment, is there a way I can delete the os without deleting all my files? I think it would probably be more convinient.
Thanks!

Why not just clone your current Windows install to the new SSD?

How To Migrate Windows 7 to a Solid State Drive
http://www.howtogeek.com/97242/how-to-migrate-windows-7-to-a-solid-state-drive/