Mohammad Darab shows how to upgrade an existing Big Data Cluster:
The above scenario was updating a Big Data Cluster from a supported release. Microsoft officially supports BDCs starting from SQL Server 2019 GDR1. But what if you have a previous version of BDCs, say CTP or release candidate? In that case you’ll have to backup any data you have, delete your cluster, uninstall azdata, install the updated azdata, and deploy your big data cluster anew. A little cumbersome but that’s how it is. In fact, no one should be running an unsupported release of Big Data Clusters anyway!
Click through for the instructions.