To assign or change the database (backend) engine that is being used to access a cluster, select a Database Cluster in the Summary Area, then choose Init => Assign Engine. The system presents a list of catalog-compatible engines. Select one and click OK.
If the desired engine is not in the list, it is because it is from an incompatible version or it is not yet known by the tool. In the former case, you need to re-initialize the cluster, as described in Section 7.6 Initializing a Database Cluster. In the latter case, you need to follow the instructions in Section 7.4 Making a Database Engine Available to make the new engine available.