Hi Rosemary, Thanks for contacting us. To achieve this you need to:
1. Drag on the dog from the Photo Basket at the bottom of the editor
2. Click the Eraser Button on the Photo Properties dialog that appears (see our eraser tool help)
3. Erase the areas of the dog photo by dragging over it with your mouse button down
If you continue to have a problem, please contact us here so that we can help you out one-on-one.