Here is how you can update a deployed container after you updated the image on Docker Hub.
First you stop the container:
docker stop <ID or name>
Then you remove the container:
docker rm <ID or name>
Then you pull the image from Docker Hub:
docker pull <image name>
Then you start a new container from the image:
docker run <image name> ...options
Of course that's not practical to do manually.
Applications like Watchtower, deployed as a Docker container, lets you setup an automated workflow for watching changes on Docker Hub (or any other image registry) and automatically gracefully shut down an existing container and restart it with the same options that were used to deploy it initially.