On the next page, you will see all of the images in your selected photo gallery in thumbnail form. These images all have a variety of action icons under them, allowing you to perform multiple operations on these images.
To change the order of images displayed in your gallery, simply use the "Move Left" and "Move Right" Green action arrows; this will move that specified image up or down in that content set's order of images.
You can repeat this step for all images in your gallery, allowing you to completely change the order that images will be displayed. Once you have finished making your changes, click "Save Tour and Thumb Changes".