• Insert your thumbnail image to the page
• Click on the image and click the 'Insert link' button
• If you have already uploaded the larger image
  • click browse server to select the image
• If you have not yet uploaded the image
  • click the upload tab browse your computer for the image and click send to server
• Click the advanced tab
• Enter a name (all one word - no spaces) for your lightbox group e.g. external_photos
• Click ok
• Save your changes
  
  When you visit the page and click on the image the large image will appear in a lightbox

Repeat these steps and use the same 'lightbox group name' to allow the visitor to click previous and next to view all large images in the lightbox.