On the same function, you can change the prompts for name, email and website by changing parameters ‘author’ , ’email’ and ‘url’ in:
$fields = array
You can edit Comment Form in wp-includes/comment_template.php
Function comment_form( $args = array(), $post_id = null )
Change parameter value of ‘title_reply’ on $defaults=array :
‘title_reply’ => __( ‘Leave a Reply’ ),
