Done. All deleted. Here’s the disk space situation:
ubuntu@discourse:/var/discourse$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/xvda1 7.8G 4.5G 2.9G 61% /
none 4.0K 0 4.0K 0% /sys/fs/cgroup
udev 996M 12K 996M 1% /dev
tmpfs 201M 356K 200M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 1001M 0 1001M 0% /run/shm
none 100M 0 100M 0% /run/user
Question is: why did I have 5 images?