By default, Docker store its persisted data (local volumes, containers, filesystem data for images, configuration for resources, swarm cluster state) in /var/lib/docker directory. To change this location to a new one, edit the file /lib/systemd/system/docker.service and adjust the entry ExecStart.

First, stop Docker service:
$ sudo systemctl stop docker
Adjust /lib/systemd/system/docker.service:
#Before (default location: /var/lib/docker): #ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock #After (new location: /opt/docker) ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock --data-root /opt/docker
[Optional] You can copy all your existing Docker data (default location: /var/lib/docker) to the new location (/opt/docker):
$ sudo mv /var/lib/docker /opt/
Reload systemd manager configuration:
$ sudo systemctl daemon-reload
Start Docker service:
$ sudo systemctl start docker
Check the new location:
$ sudo ls -al /opt/docker/ drwx------ 2 root root 4096 builder drwx--x--x 4 root root 4096 buildkit drwx------ 2 root root 4096 containers drwx------ 3 root root 4096 image drwxr-x--- 3 root root 4096 network drwx------ 3 root root 4096 overlay2 drwx------ 4 root root 4096 plugins drwx------ 2 root root 4096 runtimes drwx------ 2 root root 4096 swarm drwx------ 2 root root 4096 tmp drwx------ 2 root root 4096 trust drwx------ 2 root root 4096 volumes