To mass delete cards from a card set, follow these steps:
1. Point to the card set that contains the cards you need to delete and click Edit Set (1).
2. Click one of the cards you want to delete, press and hold the SHIFT or CTRL/CMD key and select the rest (2).
3. On the right-hand panel, click the Delete button (3).
4. On the confirmation dialog box, click Delete to delete the cards or Cancel to cancel the action.