Depends on which section you want to be bigger. Essentially, in your index.php file, you just need to add something like:
<?php if(!isset($firstPost): ?>class="first-post"<?php $firstPost = 1; endif; ?>
You can put that in your <div class="entry"> for bigger text, or in your <h2><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2> for a bigger title. Is that what you’re looking for
