Is it safe to edit wp-includes/comments-template.php
I need to edit the comments displayed on the website. I did some research and I found that in order to edit the form I have to edit wp-includes/comments-template.php. What concerns me is that this file is in the core files, an update to the CMS will replace the file causing me to loose all the changes.
What should I do.
I basically need to edit the title of Leave Reply, I wanted it in a H3, the issue could probably be resolved in CSS, but my goal is to understand WP better.