<?php defined('ABSPATH') or exit; // transfer option $options = (array) get_option('mc4wp_lite', array()); // merge options, with Pro options taking precedence $pro_options = (array) get_option('mc4wp', array()); $options = array_merge($options, $pro_options); // update options update_option('mc4wp', $options); // delete old option delete_option('mc4wp_lite');