You have to dive in to some code here.
1. Create a WordPress child theme to contain you changes so you can update the parent theme. Read more about child themes:
http://codex.wordpress.org/Child_Themes
http://wpthemetutorial.com/2012/04/26/adding-a-sidebar-to-twentyeleven-with-a-child-theme/
2. Copy index.php in to the child theme.
3. Pasted the code below over the existing loop code.
<h2>Latest Articles</h2>
<h3>Latest Articles from the Blog</h3>
<ul class="latest-posts">
<?php
// defining the arguements for the custom loop
$latestPosts = new WP_Query( array(
'posts_per_page' => 10, // neg 1 means all posts
'orderby' => 'date',
'order' => 'DESC',
)); // end query
while ($latestPosts->have_posts()) : $latestPosts->the_post();
?>
<li id="latest-post-<?php the_ID();?>"><a href="<?php the_permalink();?>" title="<?php the_title();?>"><?php the_title();?></a><span class="date">Published <?php the_time(get_option('date_format')); ?> at <?php the_time(get_option('time_format'));?></span></li>
<?php endwhile;?>
<?php wp_reset_query(); ?>
</ul>
You can then change the posts_per_page value to whatever you’d like. That will change the number of posts in the latest posts area of the site.