I am using the theme Twenty Eleven. I have uploaded a number of images to use as my headers. I am now wanting to change those images to some updated ones. When I tried to do that, it seems that I can only add new ones, but the old ones stay there. So, when I use the "random" feature, it randomizes the new images as well as the old ones. Does anyone know how to delete the old ones so they are not included in my random header selection?