For one of my sites, I wanted a more generic, gentler comment heading, so I needed to remove and/or change "Speak Your Mind." Here's how I did that.
[php]add_filter('genesis_comment_form_args', 'custom_comment_form_args');
function custom_comment_form_args($args) {
$args['title_reply'] = 'Leave a Comment'; // $args['title_reply'] = ''; for total removal
return $args;
}[/php]