In the recent versions, we try to add the functionality for changing the website time zone in the admin panel, but for earlier versions it's possible to do this by adding such line in the configuration file:(at any position, it doesn't matter):
date_default_timezone_set('Europe/London');
That's if the version of PHP which is used is 5.1 or higher. If not, it's possible to use:
putenv("TZ=Europe/London");
The list of the supported time zones may be found on: www.php.net/manual/en/timezones.php