Provided that this server is only running Discourse, you can try to run the following:
cd /var/discourse
./launcher stop app
docker rmi -f $(docker images -aq)
./launcher rebuild app
It will stop Discourse, remove all Docker images and then rebuild Discourse, which downloads our current image.
As for the accumulating files, @david do we have something like the rake s3:expire_missing_assets for local storage?