If you want to edit ” Leave a Reply or Leave a Reply to ” heading from above the Comment form in WordPress posts, do as follow:

1) Open this file : your_server_path/wp-includes/comment-template.php

2) Look for this text “Leave a Reply” on line numbers¬† 1543,¬† 1544, 1197 and 1198 . Change the text to whatever heading you want.