change featured image size

The gallery page on my http://www.toddhammerart.com/gallery site is displaying the featured images 290×150. I have went into the media settings and set the images small and medium thumbnails to 300×300. I have also tried pasting numerous codes into the functions.php file with no luck. I have also uploaded image files that are 300×300 and they show up in the thumbnails but are cropped to 290×150. I have gone through every php file in the theme and cannot find the size values to change 290×150 to 300×300. Any help is much appreciated!