To upload photos for an Item, if you want them in a specific order, then they must be named 'Anything_PhotoOrder'
IMG200_1.jpg
IMG200_2.jpg
IMG200_3.jpg etc.
If photos already exist for these item number orders, they will be overwritten.
To replace a particular photo, upload another with the specific photo order number. eg IMG200_1.jpg will replace the first photo.
If you don't require the photos in a specific order, they can be uploaded with any filename.