To delete Pcluster Manager, navigate to CloudFormation Console (deeplink) > search for
pcluster-manager > Delete. Make sure to only delete the parent stack i.e. the one without the nested badge. Nested stacks get automatically deleted in the correct order.
This will ask you to confirm.
Deleting Pcluster Manager does not delete the cluster, to delete the cluster, follow steps in b. Delete Cluster, or delete the CloudFormation stack with the same name as the cluster.