You can upgrade vSphere Replication 5.5.x and 5.6 to vSphere Replication 5.8.

To upgrade a previously installed version of vSphere Replication to vSphere Replication for Disaster Recovery to Cloud, you must mount the vSphere Replication ISO file in your environment and apply the update through the virtual appliance administration interface (VAMI) on port 5480. See Upgrade vSphere Replication by Using the Downloadable ISO Image.

If you upgrade to vSphere Replication 5.8 while the appliance is running on a vCenter Server 5.1.x, and later upgrade to vCenter Server 5.5.x, the vSphere Replication user interface might disappear from the vSphere Web Client. See vSphere Replication UI is Missing After a vCenter Server Upgrade.