Display posts in Ascending order?

I want to write my blog like a book… I want the posts to appear with the oldest one first and the newest one last. I’ve checked the dashboard and am having no luck. I know it must be simple, but I don’t understand PHP.

Can anyone help me with this? I’d really appreciate it.

Here is my template code:

<?php get_header(); ?>

<div id=”main”>

<div id=”contentwrapper”>

<?php if (have_posts()) : ?>
<?php while (have_posts()) : the_post(); ?>

<div class=”topPost”>
<h2 class=”topTitle”>“><?php the_title(); ?></h2>
<p class=”topMeta”>by <?php the_author_posts_link(); ?> on <?php the_time(‘M.d, Y’) ?>, under <?php the_category(‘, ‘); ?></p>
<div class=”topContent”><?php the_content(‘(continue reading…)’); ?></div>
<span class=”topComments”><?php comments_popup_link(‘Leave a Comment’, ‘1 Comment’, ‘% Comments’); ?></span>
<span class=”topTags”><?php the_tags(‘:‘, ‘, ‘, ”); ?></span>
<span class=”topMore”>“>more…</span>
<div class=”cleared”></div>
</div> <!– Closes topPost –>

<?php endwhile; ?>

<?php else : ?>

<div class=”topPost”>
<h2 class=”topTitle”>“>Not Found</h2>
<div class=”topContent”><p>Sorry, but you are looking for something that isn’t here. You can search again by using this form…</p></div>
</div> <!– Closes topPost –>

<?php endif; ?>

<div id=”nextprevious”>
<div class=”alignleft”><?php posts_nav_link(”,”,’« PREVIOUS ENTRIES’) ?></div>
<div class=”alignright”><?php posts_nav_link(”,’NEXT ENTRIES »’,”) ?></div>
<div class=”cleared”></div>
</div>
</div> <!– Closes contentwrapper–>