Uninstall single package
If you need to remove an installed package do the following:
apt-get remove {PACKAGE-NAME}
Or, to remove the package along with all the configuration files:
apt-get --purge remove {PACKAGE-NAME}
Clean up
If a certain package is no longer installed, its dependencies might still be active. Using autoremove the packages are removed that are no longer needed.
apt-get autoremove
List of packages
To get a list of all installed packages:
dpkg --list