1. Upon clicking on the pencil icon in the 'List Photo' page, a page similar to above will let you edit or delete particular photo.
2.You can update name, re-select category and options, modify info and view visitor comments.
3.To change your photo, click on 'View' to view thumbnail or enlarged photo before delete or you can delete it right away.
4. Now, browse to your new photo. If you check Auto Thumbnail Creation, do not browse to your thumbnail photo because a thumbnail will be generated for you automatically. The size of your thumbnail is depends on the defined size at 'Preference > General Settings'.