Increase the font size of the dropdown menu

Hi!
I am helping my Mom out by designing a website for her. For the purposes of helping me out, you can find it at…
http://www.ruthkleinbarristerandsolicitor.com/

…in the top right corner of the homepage is the dropdown menu. Currently it has the buttons “about”,”services”, and “contact us”. I would like to know how I can go about increasing the size of the font of these words.

In the theme editor dropdown.php, here is what it displays:
<?php wp_nav_menu(array( ‘theme_location’ => ‘primary’, ‘sort_column’ => ‘menu_order’, ‘menu_class’ => ‘nav-menu’, ‘container_class’ => ‘nav-menu’,) ); ?>

<div class=”clear”></div>

Please let me know if you know how I can go about increasing the font size. Thank you in advance.