Custom sidebar php to show a single category

Hi, I have taken over a website made by another person. I need to change the homepage sidebar to show only one category but the custom php that this person made, I am afraid to change it. Can anyone look at this and modify it to show only category 4?

Thank you for your help!
Diana

<h2>Recent News</h2>

<ul id="post-listing">
<?php
/**
 * Beginning of Custom WP Query
 */
$args = array(
	'post_type' => 'post',
	'post_status' => 'publish',
	'orderby' => 'date',
	'order' => 'DESC',
	'showposts' => 3,
);							

$wp_query = new WP_Query($args);

// Display returned posts
while ($wp_query->have_posts()) : $wp_query->the_post();
?>

<li>
	<h3><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h3>

	<?php $the_excerpt = substr(get_the_excerpt(), 0, 110); ?>
	<?php echo '<p>' . $the_excerpt . ' […] </p>'; ?>

	<?php /* <p>Posted in <?php the_category( ', ' ); ?> by <?php the_author_posts_link(); ?></p> */ ?>

	<p><em><?php the_time('F jS, Y'); ?></em></p>
</li>

<?php endwhile; ?>

</ul><!-- #post-listing -->