The steps are as follows:

1. Sign in to vCenter as an administrator, click Home, and then click AWS Management Portal
2. Click VPC
3. Expand the region and the VPC for the security group, and then select the security group
4. On the Getting Started tab, click Delete the security group
5. In the Delete Security Group dialog box, click Yes

You must use the Amazon EC2 console or the AWS CLI to change the security groups for a running instance.