update.php

<?php
$IdAuta=$_GET['IdAuta'];

include('laczenie.php');

$auta = mysqli_query($db,"SELECT auta.*,kolory.Kolor FROM auta INNER JOIN kolory ON auta.IdKolor=kolory.IdKoloru WHERE IdAuta='$IdAuta';");
$auto = mysqli_fetch_array($auta);

echo('<h3>Edytuj auto</h3>
            <form action="index.php?Wybor=6&&IdAuta='.$IdAuta.'" method="post">
                Marka: <input type="text" name="Marka" value="'.$auto['Marka'].'">
                Model: <input type="text" name="Model" value="'.$auto['Model'].'">
                Cena: <input type="number" name="Cena" value="'.$auto['Cena'].'">
                Kolor: <select name="Kolor">
            ');

            $kolory = mysqli_query($db,"SELECT * FROM kolory;");
            for($i=0;$i<mysqli_num_rows($kolory);$i++)
            {
                $kolor = mysqli_fetch_array($kolory);
                if($kolor['IdKoloru']==$auto['IdKolor'])
                {
                    echo("<option value='".$kolor['IdKoloru']."' selected='selected'>".$kolor['Kolor']."</option>'");
                }
                else
                {
                    echo("<option value='".$kolor['IdKoloru']."'>".$kolor['Kolor']."</option>'");
                }
            }

echo('          </select>
                <input type="submit" value="Zapisz">
            </form>')
?>