Clean up the containers and the images

docker rm myubuntu
docker rm -f myubuntu

docker rmi ubuntu:18.04

Major clean-up

Check used space

docker system df

Remove unused containers (and others) – DO WITH CARE

docker system prune

Remove ALL non-running containers, images, etc. – DO WITH MUCH MORE CARE!!!

docker system prune -a

Reference: https://www.digitalocean.com/community/tutorials/how-to-remove-docker-images-containers-and-volumes