how to add older posts 1st to this code?

Hi, id wish to add ASC to my page.
This is my index.php code, where do I add what?

<?php get_header(); ?>

<?php get_sidebar(); ?>

<div id="main">
  <div id="content">
    <?php if (have_posts()) : while (have_posts()) : the_post();?>
    <p><?php the_content(__('(more...)')); ?></p>
    <?php endwhile; else: ?>
    <p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
    <?php endif; ?>
  </div>

  </div>

<div id="delimiter"></div>

<?php get_footer(); ?>