The Dynamic Cluster is designed to support "rolling upgrades". To upgrade to a newer version of the CommuniGate Pro software, you should upgrade the Servers one-by-one: withdraw a server from the Cluster, upgrade the software, and add the server back to the Cluster. This procedure allows your site to operate non-stop during the upgrade.
Certain changes in CommuniGate Pro software can impose some restrictions on the "rolling upgrade" process. Always check the History section before you upgrade your Cluster, and see if any Cluster Upgrade restrictions are specified there.