In-place upgrade

If you want to upgrade an existing domain controller to Windows Server 2016, you need to perform an in-place upgrade. The source domain controller needs to be Windows Server 2008 or later. The in-place upgrade process doesn't perform an automatic schema and domain update; you need to run those command-line commands manually. The installation media includes the adprep.exe tool in \Support\Adprep. You need to run the following commands:

adprep.exe /forestprep
adprep.exe /domainprep

Once you have successfully performed the adprep commands, you can start by installing the upgraded operating system on a domain controller with the older OS version.

When you promote a server running Windows Server 2016 to be a domain controller in an existing domain and you have signed in as a member of the Schema Admins and Enterprise Admins groups, the AD DS schema automatically updates to Windows Server 2016.