update.php

<?php

require_once "cloudfiles.php";

// Authenticate.
$cfAuth = new CF_Authentication("username", "api key");
$cfAuth->authenticate();

// Get connection.
$cfConn = new CF_Connection($cfAuth);

// Get container.
$container = $cfConn->get_container("foo");

// Get file from container.
$file = $container->get_object("bar.txt");

// Update file in container.
$file->load_from_filename("./bar.txt");