Today I’ve play around a Virtual Machines created somedays ago, it was joined to a domain and act as a Secondary Domain Controller, so the normal dcpromo command could not let me demote it, so I need to force demote it with the following command.
dcpromo /forceremoval
/forceRemoval - Forcefully uninstalls Active Directory Domain Services on this domain controller. The account for the domain controller will not be deleted in the directory, and changes that have occurred on this domain controller since it last replicated with a partner will be lost.