Modifies the specified attribute of the specified instance. You can specify only one attribute at a time.

Note: Using this action to change the security groups associated with an elastic network interface (ENI) attached to an instance in a VPC can result in an error if the instance has more than one ENI. To change the security groups associated with an ENI attached to an instance that has multiple ENIs, we recommend that you use the ModifyNetworkInterfaceAttribute action.

To modify some attributes, the instance must be stopped. For more information, see Modify a stopped instance in the Amazon EC2 User Guide.