elseif($_GET['action'] == 'update') {
        if(empty($_SESSION['cart']) || !isset($_SESSION['cart'])) { echo 'Cos poszlo zle'; } else {
                    foreach($_SESSION['cart'] as $key=>$item) {
                        $realqty = $item['qty'] - 1;
                        mysqli_query($conn, "UPDATE items SET qty = '".$realqty."' WHERE product_index = '".$item['index']."';");
                    }
                    unset($_SESSION['cart']);
                }
    }