$re = '/server\s*=\s*\Khttps?:\/\/(?:www\.)?/';
$str = 'server=https://www.versatile-ag.ca/NA/EN/locator/locator.php';
$subst = "http://";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php