<?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' );