To delete a cluster
In the navigation pane, choose Clusters. On the Clusters page, select the cluster to delete. Choose Delete Cluster. You see a confirmation prompt.
There is no way to delete all resources in an account owned by a particular user but there is a way to delete all resources in an account. You can use aws-nuke which was created somewhat out of the same use case you described. At first, you need to set an account alias for your account.