Two ways which will help....

1) Find large files and ascertain if they can be deleted...

If you don't know where they are running something like this will help determine the location... (warning this can take awhile...)
# du -axh /* | sort -hr | head -n20

2) add more disk space to the volume by installing another disk or add unused space on an existing disk if it exists
an example https://www.clearos.com/clearfoundation/social/community/how-can-i-resize-dev-sdb#reply-145841

Disk usage app is useful to quickly find out what's consuming your volume too.

B