Step 1: Navigate into the chapter where you wish to update the image with. Once inside that chapter, click the drop-down on the top bar and then select "Main Menu Image".

Step 2: Either edit or remove the current image that is showing in this menu by clicking next to the image itself.

Step 3: Upload an image by dragging or navigating to the picture from your computer.

Once saved, you should be able to see this updated now back on the main menu image.

Note: Depending on the navigation type that your deck's menu is using, it may not be possible to edit the chapter images seen on the main menu.