x posts per page in category… – own template page

how to change this code to show only 4 posts per page in ‘www’ category?

<?php $paged = (get_query_var('paged')) ? get_query_var('paged') : 1; ?>
<?php query_posts('category_name=www&paged=' . $paged); ?>

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

<div class="bb-100" id="post-<?php the_ID(); ?>">

<h4><?php the_title(); ?></h4>
<?php the_content('Czytaj dalej &raquo;'); ?>

</div>

<?php endwhile; ?>

<div class="bb-t30 nav-entry-pages">
<div class="bb-t27 bb-fc bb-marg-nav"><?php if(function_exists('wp_page_numbers')) : wp_page_numbers(); endif; ?></div>
</div>

<?php else : ?>

<h1>error</h1>

<?php endif; ?>