How to Hide the "WunderSlider Gallery" Admin Menu

function plt_hide_wunderslider_gallery_menus() {
	//Hide the "Appearance → WunderSlider Gallery" menu.
	remove_submenu_page('themes.php', 'wunderslider-gallery');
}

add_action('admin_menu', 'plt_hide_wunderslider_gallery_menus', 11);

Where do I put this code?