Changing the leave a reply text

Hi,
I've changed this easily before in the comments.php file and I cant seem to make it work on this theme. Is there a different file I can try?
Just want to change the stand - leave a reply to - leave a comment
thanks

Hello,

This text comes from the WordPress core files, it's not recommended to change these file but if you want, you can find this text in wp-includes/comment-template.php file.