@Nancy: This plugin is not a good plugin as they have enqueue their own jquery.js instead they need to add the core WordPress jquery. They are not following WordPress guideline for development. Try to search for better plugin.
Maybe you can try removing the following code from wpng-calendar.php file. For more you need to hire customizer as this is not theme issues.
wp_enqueue_script('jquery-js', get_bloginfo('wpurl') . '/wp-content/plugins/wpng-calendar/js/jquery.js', null, '6124');
For link in Menu to open in new window. You need to build custom menu from “Appearance => Menus” then you need to assign that menu the location from “Appearance => Menus => Menu Locations”
Screenshots in Pinterest:
For custom menu: http://www.pinterest.com/pin/548594798330820987/
For link in new window: http://www.pinterest.com/pin/548594798330834738/