Sometimes it is necessary to choose a different machine in the cluster to be the primary server. Perhaps the current primary needs replacing or upgrading, for example.
If the new primary-to-be is not yet in the cluster, first add it to the cluster as a secondary server.
To select a secondary server in the cluster as the new primary, highlight it in the server list, and use the right mouse button click menu to choose "Select as primary". This menu is shown below.
Finally, if the old primary is no longer to be in use, remove it from the cluster (using "Remove Server" from the new primary's menu), and then decommission it.