For information on how to delete an AWS CloudFormation stack, see AWS CloudFormation Documentation.
Depending on how and when you provision HSNs, they may not be deleted when an AWS CloudFormation stack is deleted. If you deployed an instance prior to Teradata Vantage on AWS (DIY) 5.08, performed a software upgrade, and then provisioned HSNs, the HSNs are not automatically deleted as they are not part of the AWS CloudFormation stack. From the AWS EC2 Console, delete the auto scaling group associated with the HSNs.