For Standalone servers (the lower portion), right click on the task tray tool and click Settings. Optionally, you can launch the LocalMachineInfo editor under the Workflow Designer/Tools menu in the Start menu. In the popup that opens, click the Add button by servers to add a server. Close the dialog to save, and launch the deployment dialog again to see the new servers.
Everything in the upper part is populated via Enterprise Management on the SMP, and can't be manually changed unless you do so from the SMP.