Hi tarunb400,
thanks for using MH Purity lite.
When it comes to CSS modifications, you can always use tools like Firebug or your browsers inspection tool to inspect the elements on your site, check how the CSS has been applied and then use this information to add your own custom CSS code as you like.
To change the font size of the menu items, you could for example add this:
.main-nav li a { font-size: 16px; }
In order to apply custom CSS code, you could either create a child theme for customizations or make use of plugins like Simple Custom CSS to add custom CSS code to your website.
