Serve scaled image in portfolio section

Hi, I use your parallax frame free template. On the homepage there is the portfolio section that shows the featured images of the selected pages, but these are not scaled. In fact the source is "image.jpg", not the thumbnail "image-480x320.jpg" (existing file). The images are uploaded after installing theme and the thumbnails exist and are correct, but the template uses the original image as a source instead of the thumbnail. Could you tell me if I set it wrong or if the "serve scaled image" option is only available for the PRO version? Thank you Martina