no space left on device

I’ve been trying to get docker pull nvcr.io/nvidia/digits:18.11-tensorflow to work, with no success, so thought I’d try: docker pull nvcr.io/nvidia/digits:18.10 instead.

I seem to have run out of space! …. How do I get rid of previously pulled docker pulled things?
……… I want to get rid of 18:11-tensorflow.

Or …… How can I add more space?

Error is as below ……. Thanks!

b4ea0493c824: Waiting
94e9f6127f12: Waiting
3793c236f114: Pull complete
8dd3fee93728: Pull complete
dd8433dd186e: Pull complete
2e3137eb6a9b: Pull complete
73215a4e2c28: Pull complete
8cbb2319b813: Pull complete
bb6346a14e8a: Pull complete
b1172b11697c: Pull complete
f7d4e939e2f3: Pull complete
69fd65e359c1: Pull complete
b3073cb6c892: Pull complete
cd3cfb41069b: Extracting  475.4MB/475.4MB
60741008fcc3: Download complete
6bf9ad071f73: Download complete
c3cfc72a0228: Download complete
e5f682d39d70: Download complete
c6dc998f001d: Download complete
0789191dcf7e: Download complete
f502b222f40f: Download complete
2eb32606ef18: Download complete
78768428f5ae: Download complete
4ab52b2195eb: Download complete
2c27729d0333: Download complete
failed to register layer: Error processing tar file(exit status 1): write /usr/local/lib/python2.7/dist-packages/tensorflow/python/_pywrap_tensorflow_internal.so: no space left on device
ubuntu@ip-172-31-27-120:~$