Visit the 'Photos' tab in your Manager Portal and click the blue 'Upload a photo' button on the right.
For each category of photos (general site photos or pitch type photos), the first photo on the left is the primary (main) photo that appears in search results and/or pitch type sections.
Click on photos to drag them left or right to change the order in which photos are displayed. Please note that primary photos are only available for bookable listings.