1. Select the menu to edit 
  2. Expand the custom links section
  3. Add the URL of the page you will be linking to
  4. Click add to menu
  5. Expand the newly added Custom link
  6. In the Navigation Label section, add a link to the image in the media library
  7. The link should look like this: <img src="/wp-content/path to image here" alt="alternate text for image" />
  8. Click Save menu