If you have existing banner images on your page, you can reorder, edit or remove them when you create a new draft. At  the top of your new draft, you can see an entry for all of your existing banner images. 

The plus symbol to the left of the images allow you to drag and drop the order in which the image display on your site. When you make an adjustment to the order, the yellow warning will appear over the section telling you that changes will not be saved until you publish you page.
You can also remove or edit existing banner images using the buttons on the right of each image.