You can check if the cluster is in use by:

1. Logging in to Azure Databricks Workspace

2. Go to compute (on the left hand panel)

3. For each cluster listed you can check whether it is running and the last activity

   1. For each cluster you can check if it has not run any jobs recently. If that is the case, it may be safe to delete it

4. To delete a cluster you would need to terminate it first. Only terminated clusters can be deleted. There is a good tutorial over here:

   1. https://www.chaosgenius.io/blog/databricks-clusters/