Assuming you have been working and testing on a OS X Server and decided that you need to start at fresh, this is an easy way to hose your system back to square one without having to do a complete reinstall.
Open up Terminal on your Mac Server
Type: sudo rm /var/db/.ServerSetupDone
This will hose the server app settings and get you back to the beginning!!
I myself have used this many times, to save me from re installing OS X 10.8 and then the Server App.