On your post/page editor screen, look for "Discussion" panel and uncheck the "Allow comments" option.
if you like to remove it from comment option completely then you can go to theme and find page.php or content-page.php and find <?php comments_template(); ?> make it like <?php //comments_template(); ?> so it will not show the comment box. If you can tell us which theme you use then we can tell you more specific. thanks