<?php

// The directory that contains the files that you want to rename to lowercase
$directory = "/public_html/media/catalog/product/s/t/";

$conn = ftp_connect("website");
ftp_login($conn,"username","password");

ftp_pasv($conn,true);

ftp_chdir($conn,$directory);
$dir = ftp_nlist($conn,".");

foreach($dir as $fsObject)
{
    if($fsObject != "." || $fsObject != "..")
    {
        if($fsObject != strtolower($fsObject))
        {
            ftp_rename($conn,$fsObject,strtolower($fsObject));
            echo strtolower($fsObject)."<br>";
        }
    }
}

ftp_close($conn);
echo $directory."<br>";
echo "Finish!";

?>