[ Thanks to kiterunner for this link.
]
“When you install something in Ubuntu, package files
are downloaded for installation but are not automatically deleted
after installation is over. Instead the files will be used as a
backup in case the application needs a reinstall in the future. But
in most cases, this is a sheer waste of space especially if you are
using a old laptop or a netbook with minimal amount of disk space.“There are a number of ways in which you could actually do the
cleaning up operation of your Ubuntu desktop. Ubuntu Tweak is an
awesome tool and its quite easy to free up disk space in Ubuntu
using Ubuntu Tweak. But if you don’t want to install another
application to do the cleaning up, you have two ways to do it. One
is the command line option(recommended) and other is by using
Synaptic Package Manager.”