What is the next step after locating the FSMO roles when upgrading an existing Active Directory Domain Services (AD DS) forest?

The next step after locating the FSMO (Flexible Single Master Operation) roles during an upgrade of an Active Directory Domain Services (AD DS) forest is to transfer those roles to a new domain controller. FSMO roles are critical to the functioning of AD DS, and during an upgrade, it is important to ensure that these roles are managed correctly to maintain the integrity and availability of the directory services.

Transferring the FSMO roles to a new domain controller helps distribute the load and enhances fault tolerance. It ensures that the new domain controller is equipped to handle important tasks like schema updates, domain name resolution, and DC registration, which are vital during and after the upgrade process. By doing this, you also allow for the decommissioning of older or outdated domain controllers without impacting the operational capacity of the Active Directory infrastructure.

The other options would not be appropriate immediate steps in this context. Deleting the old domain controller, rebooting the existing domain controller, or merely documenting the existing roles do not contribute directly to a safe and effective upgrade process. Instead, transferring the roles ensures that control is maintained and that the new setup is ready to take over all necessary functions.