Adjusting slider or gallery to automatically fit images

At work, I have been charged with updating our website http://www.mkarchmtl.com . We are using Revival theme by Viva Themes. Some of the images in the front page gallery are laid out in portrait instead of landscape. Is there a way I can have the gallery automatically adjust to fit the height of the image? Currently all of the images are set at 800px wide x 500px high. I want to invert those dimensions for the portrait images and have the bottom border of the gallery drop down to fit the image and also center the image. Please HELP!