Hi akole,
To shrink the height of the main menu Go to Appearance -> Theme Options -> Design Options Tab -> Custom CSS paste the following CSS code and Click on save all changes button:
#access a {
height: 35px;
padding-top: 16px;
}
#access a:hover,
#access ul li.current-menu-item a,
#access ul li.current_page_ancestor a,
#access ul li.current-menu-ancestor a,
#access ul li.current_page_item a,
#access ul li:hover > a {
padding-top: 11px;
}
#access ul li ul {
top: 51px;
}
Thank you!