An Auto Scaling group uses a launch template. Operations creates a new template version with a patched AMI and configures the group to use it. Existing instances still run the old AMI. Which action performs a controlled replacement of the existing fleet?

1. Run a scheduled action that keeps desired capacity unchanged and assume existing instances adopt the new template.
2. Delete the old AMI immediately and assume the group replaces instances because their AMI no longer exists.
3. Wait for the launch-template update to alter the operating-system disk of every running instance in place.
4. Start an instance refresh with the desired launch-template version and appropriate healthy-capacity and warmup settings.