if (ISSET($_POST['submit'])) {
    if (ISSET($_FILES)) {
        $img = $_FILES['img']['name'];
        $img_name = time().'_'.$_FILES['img']['name'];
        $img_tmp_name = $_FILES['img']['tmp_name'];
        $img_type = $_FILES['img']['type'];
        $image_dir = "images/";
                // find previous image
                $query = "SELECT `image` from `imag` WHERE id = $id LIMIT 1";
                if ($result = mysqli_query($query)) {
                    if (mysqli_num_rows($result) == 1) {
                        $row = mysqli_fetch_assoc($result);
                        $previous_image = 'images/'.$row['image'];
                        if (file_exists($previous_image)) {
                            unlink($previous_image);
                        }
                    }
                }
        $query = "UPDATE `imag` SET `image` = '$img_name' WHERE id = $id";
        echo $query;
        // if (move_uploaded_file($img_tmp_name,$image_dir.$img_name)) {
            // if(!$run = mysqli_query($con,$query)) {
                // $error = 'Update Fail';
            // }
        // } else {
            // $error = 'Fail to upload';
        // }
    }
}