ah ok era per non mettere troppo codice
Codice PHP:
<html>

<?php

        include("config.php");

        

        if(!isset($_FILES["files"]["tmp_name"]) || empty($_FILES["files"]["tmp_name"])){

                                

                $utente=$_SESSION['username'];            

                $id=$_SESSION['idpo'];

                $idpo= $_POST['idpo'];        

                $numero= $_POST['numero'];

                $co= $_POST['co'];

                $note= $_POST['note'];

                $idcliente= $_POST['idcliente'];

                $c= $_POST['c'];

            

                $query = "UPDATE po SET idpo='$idpo', numero='$numero', co='$co', idcliente='$idcliente', note='$note', c='$c', utente='$utente', data=SYSDATE() WHERE idpo='$id'";

                mysql_query($query) or die (mysql_error());                

                ?>
...
<?php
}else{

                // controllo che non ci siano stati errori durante l'upload

                if (!is_uploaded_file($_FILES["files"]["tmp_name"]))

                    die ("Errore di caricamento: ".$_FILES["files"]["error"]);

    

                    $nome = $_FILES["files"]["name"];

                    $dimensione = $_FILES["files"]["size"];

                    $cartella = "po/";

                    if($dimensione < 10240000000) {



                        if(is_file($cartella.$nome)){

    

                            echo "Esiste gi� una doc con questo nome";

        

                        }

                        else {

                            $c=$_SESSION['c'];

                            $utente=$_SESSION['username'];    

                            $id=$_SESSION['idpo'];

                            $idpo= $_POST['idpo'];        

                            $numero= $_POST['numero'];

                            $co= $_POST['co'];

                            $note= $_POST['note'];

                            $idcliente= $_POST['idcliente'];

                            $c= $_POST['c'];

        

                            // sposto il file caricato nella cartella di destinazione

                            $po= move_uploaded_file($_FILES['files']['tmp_name'], $cartella.$nome ) or die("Errore di upload del file.");

              

                            $query = "UPDATE po SET idpo='$idpo', nome='$nome', numero='$numero', dimensione='$dimensione', co='$co', idcliente='$idcliente', note='$note', c='$c', utente='$utente', data=SYSDATE() WHERE idpo='$id'";

                            mysql_query($query) or die (mysql_error());

                        }//fine else

                    }//fine if dimensione                

                

                            ?>
Ecco quanto richiesto