How to change 'Leave a Comment' or 'Reply'

Hi katieprops

Glad you like it.
The text strings you mentioned are default by WordPress. I didn’t customize. You could do the following:

Open comments.php and change line no 53 to
wp_list_comments( array( 'reply_text' => 'YOUR TEXT FOR REPLY BUTTON', 'callback' => 'albinomouse_comment' ) );

and change line no 74 to
<?php comment_form( array( 'title_reply' => 'YOUR TITLE TEXT' ) ); ?>

You’ll find more informations here:
http://codex.wordpress.org/Function_Reference/comment_form
http://codex.wordpress.org/Function_Reference/wp_list_comments

Warning!
If you customize any of the original files, it can be overwritten during a theme update. I recommend you to backup your changes or create a Child Theme.

Cheers Stefan