From http://wp-snippets.com/addremove-wp-admin-bar-links/

Remove Admin Bar Items

//Remove Admin Bar Items
function mytheme_admin_bar_render() {
    global $wp_admin_bar;
    // we can remove a menu item, like the Comments link, just by knowing the right $id
    $wp_admin_bar->remove_menu('comments');
    // or we can remove a submenu, like New Link.
    $wp_admin_bar->remove_menu('new-link', 'new-content');
    // we can add a submenu item too
    $wp_admin_bar->add_menu( array(
        'parent' => 'new-content',
        'id' => 'new_media',
        'title' => __('Media'),
        'href' => admin_url( 'media-new.php')
    ) );
}
// and we hook our function via
add_action( 'wp_before_admin_bar_render', 'mytheme_admin_bar_render' );