Pleas note that the Domain Name can only be changed by uninstalling the active directory service.
To demote the server
1. Click Start and then click Run.
2. In Open, type dcpromo.
Running the Active Directory Installation wizard will demote this server to be a member server
or stand-alone server depending on what type of domain controller this is. Before you proceed,
be sure there are no dependent servers connected to this server.
After restarting the server install active directory by running the command "dcpromo" and change domain name as desired. After completion of directory service you need to restart the server once again.