You can delete stamps you no longer need from the Presets list.
 How to delete a stamp.
How to delete a stamp.
                                                            - In the Tools toolbar, select the Stamp tool. 
- In the Presets list of the Tool Properties view, select the stamp you want to delete.
- Click on the Delete Brush button just above the Presets list. 
The stamp is removed from the Presets list.