When you no longer need a domain controller, you can decommission it and remove it from service. Running the Active Directory Domain Services Installation Wizard (Dcpromo.exe) on the domain controller allows you to remove Active Directory Domain Services and demote the domain controller to either a stand-alone server or a member server.
The process for removing an additional domain controller is different from the process for removing the last domain controller. If the domain controller is the last in the domain, it will become a stand-alone server in a workgroup. Otherwise, if other domain controllers remain in the domain, the domain controller will become a member server in the domain.