Follow these steps to change the domain name in Active Directory:

1. Verify if all clients in your network environment are capable of handling a Domain Name System (DNS) name change.
2. Ensure that you have a backup of your Active Directory database prior to making any changes.
3. Stop all replication of the domain by using the Sites and Services console and deselecting the replication setting.
4. Change the domain name using the Active Directory Domains and Trusts snap-in.
5. Once the domain name is changed, you must apply the new domain name settings into the appropriate registry entries in all client computers in the network.
6. Create the necessary DNS records for the new domain.
7. Restore and activate replication of the domain.