If you no longer need a card, you can delete it from either the Bookshelf (in full-screen view) or from the Source list.
To delete a card from the Bookshelf:
In full-screen view, navigate to the main view.
To get to the main view, you may need to click the All Events, All Faces, Projects, or other navigational button in the top-left corner of the window.
In full-screen view, the main view contains five navigational buttons for the Events, Faces, Places, Albums, and Projects views. The content shown corresponds with the selected button.
Click the Projects button in the toolbar.
The Bookshelf appears, displaying your books, cards, and calendars.
Press the Control key while you click the card, and then choose Delete Card from the shortcut menu.