Is there any software for visual display of disk space?
Solution 1:
My personal favorite is GNOME Disk Usage Analyzer (baobab):
You can install it with
sudo apt-get install baobab
Select any file from the table on the left side to move it to trash on right click.
Solution 2:
There is a fully rewritten version of KDirStat, by the same author, named QDirStat. Fast, customizable, using Qt5, desktop-agnostic (not depending on KDE components), and showing a squared view rather than concentric circles, which I personally find clearer. There is a ppa available for the installation.