if (isset($_POST['update_sub_categories']))
    {
    $file = $_FILES['Subcategory_image']['tmp_name'];

    this are the conditions for update images
    if (file_exists($file))
        {
        $errors = array();
        $maxsize = 2097152;
        $acceptable = array(
            'image/jpeg',
            'image/jpg',
            'image/gif',
            'image/png'
        );
        if (($_FILES['Subcategory_image']['size'] >= $maxsize) || ($_FILES["Subcategory_image"]["size"] == 0))
            {
            $errors[] = 'File too large. File must be less than 2 megabytes.';

            // code...

            }

        if (!in_array($_FILES['Subcategory_image']['type'], $acceptable) && (!empty($_FILES["Subcategory_image"]["type"])))
            {
            $errors[] = 'Invalid files type. Only JPG, GIF and PNG types are accepted';
            }
        }

if (count($errors) === 0)
        {
        move_uploaded_file($_FILES['Subcategory_image']['tmp_name'], 'images/categories/' . $_FILES['Subcategory_image']['name']);
        $Subcategory_image = $_FILES['Subcategory_image']['name'];

        // code...

        $m->set_data('Category_id', $Category_id);
        $m->set_data('Subcategory_description', $Subcategory_description);
        $m->set_data('Subcategory_name', $Subcategory_name);
        $m->set_data('Subcategory_image', $Subcategory_image);
        $a = array(
            'Category_id' => $m->get_data('Category_id') ,
            'Subcategory_description' => $m->get_data('Subcategory_description') ,
            'Subcategory_name' => $m->get_data('Subcategory_name') ,
            'Subcategory_image' => $m->get_data('Subcategory_image') ,
        );
        $q = $d->update("sub_categories", $a, "Subcategory_id='$Subcategory_id'");
        if ($q > 0)
            {
            header("location:Manage_subcategories.php");
            }
          else
            {
            echo "Error";
            }
        }
      else
        {
        header("location:Manage_subcategories.php?msg=invalidfile");
        }
    }