You can use the dpkg command to see a list of all installed packages on your computer.
dpkg --list
To uninstall a program use apt command. For example, the following command uninstall gimp
and deletes all the configuration file, using the --purge command.
sudo apt --purge remove gimp
If you don't want to remove the configuration files, simply leave out the --purge command,
as shown int the following command.
sudo apt remove gimp
When you uninstall a program, there may be packages that the uninstalled program depended upon
that are no longer used. To remove nay unused packages, use the automove command, as shown in the following command.
sudo apt autoremove
You can combine the two commands for removing a program and removing
dependencies that are no longer being used into one, as shown below.
sudo apt purge --auto-remove gimp
If you're short on space, you can use the clean command to remove downloaded archive files,as shown below.
sudo apt clean
This command removes the aptitude cache in /var/cache/apt/archives.
When you install a program, the package file is downloaded and stored in that directory.
You don't need to keep the files in that directory. However, the only drawback of deleting them,
is that if you decide to install any of those programs again, the packages would have to be downloaded again.
Reference:
How to Uninstall Software Using the Command Line in Linux