Your navigation menu has a panel area devoted to it within the Design tool. See below on changing the look of your navigation menu.
1. Select Design in the Dashboard navigation bar.
2. Select Navigation under the Sitewide tab in the righthand Design panel.
3. Use the options in the Text panel to change your font selection, text color, capitalization, character spacing, and alignment.
4. Select the green Save and Publish buttons to make it live to your site now.