Andrew on "How to i align the navigation bar to the centre ?"

If you're not using a Child Theme, and if the theme doesn't have a designated section of the dashboard for CSS modifications then install this Custom CSS Manager plugin http://wordpress.org/plugins/custom-css-manager-plugin

Then use its "CSS Code" section of the dashboard to hold your CSS modifications:

Alternatively use your Child Theme style.css file to hold your CSS modifications:

.main-navigation .current-menu-item > a, .main-navigation .current-menu-ancestor > a, .main-navigation .current_page_item > a, .main-navigation .current_page_ancestor > a {
    color: #000;
    font-weight: 400;
}