How to I change the featured image functionalit...

At the top of each of the content-xxxxxxx.php files you will see $ft_image_atts which is an array of settings you pass to the function.

$ft_image_atts = array( 
    'fallback_to_first_attached' => true,
    'thumbnail_size' => 'twelve',
    'full_size' => 'full',
    'linkto' => 'file',
    'hide_on_single' => false
);
echo cudazi_featured_image( $ft_image_atts );