If you're doing any kind of Active Directory® directory service or Active Directory Domain Services (AD DS) upgrade, you might want to look at restructuring your environment. And if you do, the tool you need is the Active Directory Migration Tool v3.1 as well as the Active Directory Migration Tool v3.1 Guide.
There are a couple of reasons you might want to do this. First, you might want to go optimize your active directory implementation, such as simplifying your domain structure or you might be in the process of a merger, acquisition, or divestiture and need to merge different forests or break pieces of the forest off.
Restructuring involves the migration of resources between Active Directory domains in either the same forest or in different forests. After you deploy Active Directory or AD DS, you might decide to further reduce the complexity of your environment by either restructuring domains between forests or restructuring domains within a single forest.
The Active Directory Migration Tool also allows you to perform object migrations and security translation as necessary so that users can maintain access to network resources during the migration process.