When packages are installed the corresponding .deb files are stored in /var/cache/apt/archive. This can become quite populated with older versions of packages and we can clean out these older versions with:
$ wajig autoclean (apt-get autoclean)
Warning: It is sometimes useful to have older versions of packages hanging around if you are tracking the unstable release. Sometimes the newer versions of packages are broken and you need to revert to an older version which is generally not available from the Debian archives, but might be in your local download archive.
Nonetheless, if you get short of disk space then you might want to remove all the downloaded .deb files (not just the older versions of downloaded files) with:
$ wajig clean (apt-get clean)
To remove files immediately after they have been installed edit /etc/apt/apt.conf:
// Things that effect the APT dselect method DSelect { Clean "auto"; // always|auto|prompt|never };