for automatic update create a file in the root directory cron.php
with code:
<?php
include(dirname(__FILE__).'/config/config.inc.php');
include(dirname(__FILE__).'/classes/Currency.php');
if (isset($_GET['secure_key']) AND $_GET['secure_key'] === 'password')
Currency::refreshCurrencies();
?>
change password as you like, for exampe 23Ab09Ce etc.
After that in your server control panel create a crontab with name for example Currency
and use file URL http://www.yoursite....php?secure_key=password
And set the time you want for automatic start of this file (all weekdays, all months, all days, chose the hours and minutes).
NB! Rates are usually updated by 3 p.m. C.E.T by Europen Central Bank