How to Hide PostExtra Admin Menus

function plt_hide_post_extra_menus() {
	//Hide "Post Extra".
	remove_menu_page('pxtr-admin');
	//Hide "Post Extra → Post Extra".
	remove_submenu_page('pxtr-admin', 'pxtr-admin');
	//Hide "Post Extra → Contact Us".
	remove_submenu_page('pxtr-admin', 'pxtr-admin-contact');
	//Hide "Post Extra → Support Forum".
	remove_submenu_page('pxtr-admin', 'pxtr-admin-wp-support-forum');
	//Hide "Post Extra → Upgrade".
	remove_submenu_page('pxtr-admin', 'pxtr-admin-pricing');
}

add_action('admin_menu', 'plt_hide_post_extra_menus', 1000000000);

Where do I put this code?