how to schedule the managed image updates in appstream

Here is a blog on how to schedule managed image updates https://aws.amazon.com/blogs/desktop-and-application-streaming/scheduling-managed-image-updates-for-appstream-2-0/

You will need to update your fleet after testing / validating the new image works properly.

edit - Here is another blog on automating the image deployment https://aws.amazon.com/blogs/desktop-and-application-streaming/how-to-automate-amazon-appstream-2-0-image-deployment/