The issue is most likely due to images being resized to specific dimensions with a fixed aspect ratio. The default image sizes are defined in the settings -> media section of admin of within the theme — If the images are defined here, uncheck the option labelled: "Crop thumbnail to exact dimensions (normally thumbnails are proportional)"
Often themes also define additional featured image sizes and can set whether the crop is to an exact size or not. This is usually in the functions.php however as you are using a commercial theme (the forum policy is that commercial themes are supported by their vendor/author, not here), you will need to get support from the vendor to find out how to change this if you are unable to find it easily. The code may resemble the examples at http://codex.wordpress.org/Function_Reference/add_image_size