To edit files in WordPress you need to do it by either viewing your website files after connecting to your web server with an FTP client such as FileZilla, or by using a File Manager in your hosts cpanel or similar.
Or, you can edit Theme files from the Appearance: Editor menu on the WordPress Dashboard.
Editing files can break your theme, or WordPress install depending on where you edit. Backup all files before carrying out any modifications so you can revert back. Modifying through an FTP client just makes things a bit easier, especially if a bad edit breaks WordPress and you can no longer access the Dashboard Editor.
Editing Themes and WordPress isn't easy if you don't know HTML/CSS/PHP to some extent, and this is why people often actually employ people to fix things. Anyway...
Onto editing the files, it really depends on the Theme you use. The instructions for each theme can be different. It's not a set list of instructions as such, as they are written by different people. Without knowing your theme or website URL I can only give brief instructions.
<? php comments_template(); ?> ? is what calls your comments template. This will be located in a certain file in your themes folder. For a page, it may be in page.php for example. For a post, it may be in single.php. It's hard to say. By removing this it'll stop calling the comments template, however that may lead onto css styling issues.
You might get better luck posting in that particular themes forum for help :)