can't upload image

What am I missing here, take a look at: example database, I can only upload from my computer or make a change from my computer. How do I edit a record and change the image name from another computer, or how can a user in general do it. On the sample above, first click pets, then show all, and try to edit the record ANOTHER PET. Try to change the image name from hunt.jpg to briggs.jpg. The images are already uploaded to the demo account, but I can't figure how to add or edit a record (image part) where the images are on the server. What if this was a general public database where users were to edit and add records???