Before upgrading make sure both nodes have been synchronized. Then stop the MOVEit Central service on both nodes (using MOVEit Central Admin's "Shut Down Service" command on the primary node). Once the services have been stopped on both nodes run the upgrade on the primary node first and make sure the MOVEit Central service is started on this node before upgrading the secondary node. (By upgrading the primary node first no unnecessary failover will occur.)
After the upgrade, you may receive an email from one or both MOVEit Centrals reporting that they could not contact the other Central node. This is a result of having the service running on one node and not the other during the upgrade process. This message can safely be ignored.
Windows updates can normally be applied without shutting the MOVEit Central services down. However, if a reboot is required by a Windows update package, plan to take down the MOVEit Central service on the secondary node, then boot the primary node and let it come back up before rebooting the secondary node. (Make sure the secondary node also brings its MOVEit Central service up after its reboot.)