A security group should always have attached protected assets. Removing Unused Security Groups is the expected outcome of the firewall and router rule sets review.
Deleting a Security Group : To delete a security group using the console
1. Open the Amazon VPC console at https://console.aws.amazon.com/vpc/.
2. In the navigation pane, choose Security Groups.
3. Select the security group and choose Security Group Actions,Delete Security Group. 4. In the Delete Security Group dialog box, choose Yes, Delete.
Via CLI :
aws ec2 delete-security-group –group-id sg-<