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There is one more way to achieve this, without overriding files, using functions.php.
Add following code in functions.php file.

add_filter('wp_list_comments_args', 'override_args', 10, 1);

function override_args($args)
{
   $args = array(
                 'style'       => 'ol',
                 'short_ping'  => true,
                 'avatar_size' => 56,
                 'per_page' => '3'
                );
   return $args;
}