opti-slider.php

<?php
/**
 * Plugin Name: Change Opti slide quantity
 * Plugin URI: https://prothemedesign.com
 * Description: Change number of posts that appear in the Opti slider.
 * Author: Ben Gillbanks
 * Version: 1.0
 * Author URI: https://prothemedesign.com
 * Text Domain: opti
 */

function opti_slider( $params ) {

	$params['max_posts'] = 5;
	return $params;

}

add_filter( 'opti_featured_content', 'opti_slider' );