If you want to change the sequence of the photos in your apartment, go to your Control Panel - section Apartments - All apartments, and select the apartment that you need, and click Edit.
In the editing window, skip to 3rd step. You'll see all the pictures that you've added to the apartment. If you want to change the order or to change the main image that is displayed on the catalog page of the site, use the arrows under the pictures.
When you are clicking on the arrow "right" and "left" on a particular photo, you change its order. For example, you press the "right" arrow and this means that the picture will be in one position farther. If you press the "left", it is moving to a position that is closer to the title picture.
Do not forget to save your changes.
Photo, which is displayed as the biggest in Step 3 is the first picture of your apartment, which users will see in the catalog site. It will look like this: