You can easily upload photos and videos of your items from Menus.
Click on Edit to open the Item Detail page. Drag&drop a file inside the relevant box OR click "Browse" and select the file from your computer.
When your photos are loaded, you can click the "Publish" button on the top of the page and your tablets will be refreshed. Please be sure that you have a proper internet connection for this, otherwise your changes will not be reflected in your menu.