When a quiz is no longer needed you can either hide it so that it is not visible to users, or delete it completely.
To hide a quiz locate it within the card set and check its checkbox (1). You can then either hide (2) or delete it (3).
Alternatively, you can hover over the Quiz, click on the3-dot symbol (4), and then select Delete (5).
Find out how you can add a new quiz to a card set here.