In the DDS, you can modify the security group of an instance in the following steps:
Go to the DDS Management Console.
Click the Instance Management menu to go to the instance list page.
Select the instance for which you want to modify the security group, and click the instance ID to go to the instance details page.
Locate the Security Group information in the Network section and click Edit (The button is the Modify link instead for some resource pools).
In the Edit Security Group pop-up window, select the security group you want to modify, and click OK. The security group is modified.