Docker complains about "no space left on device", how to clean up?

I installed docker on a Debian 7 machine in the following way

$ echo deb http://get.docker.io/ubuntu docker main > /etc/apt/sources.list.d/docker.list$ sudo apt-get update$ curl -sSL https://get.docker.com/ubuntu/ | sudo sh

After that when I first tried creating an Image it failed with the following error

 time="2015-06-02T14:26:37-04:00" level=info msg="[8] System error: write /sys/fs/cgroup/docker/01f5670fbee1f6687f58f3a943b1e1bdaec2630197fa4da1b19cc3db7e3d3883/cgroup.procs: no space left on device"

Here is the docker info

Containers: 2Images: 21Storage Driver: aufsRoot Dir: /var/lib/docker/aufsBacking Filesystem: extfsDirs: 25Dirperm1 Supported: trueExecution Driver: native-0.2Kernel Version: 3.16.0-0.bpo.4-amd64Operating System: Debian GNU/Linux 7 (wheezy)CPUs: 2 Total Memory: 15.7 GiBWARNING: No memory limit support WARNING: No swap limit support

How can I increase the memory? Where are the system configurations stored?

From Kal's suggestions:

When I got rid of all the images and containers it did free some space and the image build ran longer before failing with the same error. So the question is, which space is this referring to and how do I configure it?