Hi Rob,
You need to edit functions.php line 88:
add_image_size( 'full-width-image', 1000, 563, true);
Simply set the image size to be a max value you’d want the slider height to be, and it will then follow that. You’ll need to re-upload the images, or use the Thumbnail Regeneration plugin to re-create the image sizes after the change.
– Ed