Resetting Old License
If you have a machine that no longer needs to be backed up, but has an agent that is currently acquired, it can be reset from the edit license screen.
To do this, click on Manage>Licensing>Edit License.
Expand the agents until you see the server name that needs to be reset.
By right-clicking on the server name you will be given an option to reset the license.
Once that license has been reset, it will be available to be acquired by a new machine name, when a backup of that machine is run.