Official docker page https://docs.docker.com/engine/installation/linux/ubuntulinux/#uninstallation
sudo apt-get purge -y docker-engine
sudo apt-get autoremove -y --purge docker-engine
sudo apt-get autoclean
The above commands will not remove images, containers, volumes, or user created configuration files on your host. If you wish to delete all images, containers, and volumes run the following command:
sudo rm -rf /var/lib/docker
Remove docker from apparmor.d:
sudo rm /etc/apparmor.d/docker
Remove docker group:
sudo groupdel docker
Now, You have successfully deleted docker.