How do you delete applications which are stored in your system preferences?
You can check if its related files are still stored in your computer. Activate Finder, then click Go > Go To Folder, and type in /Users/yourusername/Library/Application Support, replacing yourusername with your username. From here, you will be able to remove your application's related files.

You can remove the application's Preference Pane from System Preferences by opening System Preferences and right-clicking the application's name, and click "Remove Preference Pane".