Some times need to change the default product image that appears on product catalogue and on the checkout page.
It is possible to do by the following steps:
1) Open the product that you want to change in the Custom Product Builder admin panel.
2) Click on "Actions" button and choose "Edit product in Shopify":
3) On the page that opens you can remove the old image and add the new one. After that click on the "Save" button on the top or bottom of the page: