On Windows Server 2012, administrators cannot perform "dcpromo" to demote a domain controller. To demote a domain controller, administrators can use "Server Manager" or "PowerShell".
I will demote a domain controller on Windows Server 2012 by GUI.
Assuming that there is 1 domain controller named DC01 in "fabrikam.com" domain.
1. On DC01, log in as Domain Administrator.
2. Launch "Server Manager".
3. On "Server Manager", click "Manage".
4. Select "Remove Roles and Features".
5. On "Before you begin" screen, click "Next".
6. On "Server Selection" screen, select "DC01.fabrikam.com".
7. Click "Next".
8. On "Server Roles" screen, clear the "Active Directory Domain Services" check box. Then you will see the following window.
9. Click "Remove Features".
10. Then you will see the following window and then click "Demote this domain controller".
16. Click "Next".
17. On "New Administrator Password" screen, provide a new password for the local administrator.
11. On "Credentials" screen, check "Last domain controller in the domain".
Because there is 1 domain controller in my environment, I need to check "Last domain controller in the domain". If there is more than 1 domain controller in your environment, you don't need to check this option.
Remark: On Windows Server 2012, "Force the removal of this domain controller" is instead of "dcpromo /forecremoval".
Remark: On Windows Server 2012, "Force the removal of this domain controller" is instead of "dcpromo /forecremoval".
12. Click "Next".
13. On "Warnings" screen, check "Proceed with removal".
13. On "Warnings" screen, check "Proceed with removal".
14. Click "Next".
15. On "Removal Options" screen, check "Remove the DNS zone (this is the last DNS server that hosts the zone)", "Remove application partitions".
Remark: If your environment is more than 1 domain controller, you don't need to check the above options, ("Remove the DNS zone (this is the last DNS server that hosts the zone)" and "Remove application partitions").
16. Click "Next".
17. On "New Administrator Password" screen, provide a new password for the local administrator.
18. Click "Next".
19. On "Review Options" screen, click "Demote".
20. When the demotion finished, the server will restart automatically.
As a result, the domain controller has been demoted.
