When editing a Page of a Document, you can re-order the photos via drag-and-drop.  

To drag and drop the photos into the desired order, place the pointer on the photo you would like to move. Press, and hold down the button on the mouse or other pointing device, to grab the object. Drag the photo to the desired order by moving the pointer and then release the button.

If you need further assistance or have additional questions please contact support@umapped.com