how to upgrade a docker container after its image changed?

• https://stackoverflow.com/questions/26734402/how-to-upgrade-docker-container-after-its-image-changed
• https://hub.docker.com/r/sameersbn/gitlab/ – the Docker container image’s home page

I am using a Docker container for a GitLab CE installation. The GitLab installation inside tells me “update asap“. How do I deal with that?

• should I wait for an update of the Docker container image? (that’s what the article title refers to)
• will that update preserve my data already living inside the container?
• alternatively: how to update the GitLab installation myself? (I find the update request rather urgent)
• https://docs.gitlab.com/omnibus/update/README.html#zero-downtime-updates – instructions for zero downtime updates

I wasn’t able to find any gitlab related APT / Debian package I could even try to update.