How to update task definition with least interruption to the service?

I have an ECS service running tasks on Fargate. I have multiple tasks running for the service during the time I want to introduce a change in memory. Let's say currently they are 1GB but the latest definition will be 2GB memory. When I change the service to point to the new definition, it creates a new set of tasks, and then immediately kill the old tasks with the old definition. Is there a way to do it gracefully part of the task autoscaling life cycle?

Note that all my tasks health status showing as unknown. Did not give it so much thought, but would that be a reason or replacing all tasks for a new definition is expected?