You need to delete it one by one.
If you have many background and graphics sprites, you can add all the images in one sprite and make the animation speed to 0 , then change the frames as you like.
This better than using 50 sprites as background and graphics.
Oh, so there is no way to delete it automaticaly
How to add them into 1 sprite? Using 3rd party image editor like PS or FW right?