To login to the ASE plug-in see instructions starting with the Setting the Environment and Starting Unified Agents topic.
This means that the old server must run on the same system as the one that the UAF agent for the Cluster Edition runs on, and on which the newly upgraded cluster will reside.
After you install the Cluster Edition, start the Adaptive Server plug-in and make sure you can view the old server icon in the left pane. Connect to the old server the same way you would connect to a Cluster Server. See the Connecting to the Cluster topic for more information.