First of all I would really like do discourage you from using the file editor. One simple spelling mistake like a missing ; can completely whitescreen your site and make it inaccessible. You would then need to use ftp to get to your site and correct your error from there in order to be able to log in again.
If you are very unfamiliar with code, the easiest route would be to use a custom css plugin like Simple custom css or Custom css manager. There you can paste this piece of code to hide the comment metadata:
The code can also be added to your child theme’s style.css file instead of using a plugin. There are other ways to get rid of it involving php code in the theme files, but this is the easiest and simplest solution.