This tutorial will explain how to install and configure Active Directory (AD DS) under Windows Server 2012
http://sharepointgeorge.com/2012/configuring-active-directory-ad-ds-in-windows-server-2012/
If you by accident configured you Active Directory (AD) with a wrong domain controller, you can demote / remove if by navigating to server roles > Remove Roles and Features > Active Directory Domain Services > Next, and you’ll be prompted with a validation error, where you can click “Demote this domain controller”. Choose this option and run the wizard. This will not uninstall the Active Directory service itself, but only the installed domain controller (domain.com).
http://techibee.com/active-directory/demoting-a-active-directory-domain-controller-in-windows-2012/1836