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After removing, installing new or upgrading packages, there can be some packages not needed any more.
They can be safely removed from the system. Every command has to be run with super user privileges sudo.
sudo apt-get autoremove
After upgrading packages, the package manager keeps all deb packages even if doesn't need them any more.
To remove all old deb packages from the system (the latest deb versions will be NOT removed), run:
sudo apt-get autoclean
If you would like to remove all the deb packages from the system, run:
sudo apt-get clean