Custom fields at the bottom

<?php
/**
 * @package    HikaShop for Joomla!
 * @version    1.5.8
 * @author    hikashop.com
 * @copyright  (C) 2010-2012 HIKARI SOFTWARE. All rights reserved.
 * @license    GNU/GPLv3 http://www.gnu.org/licenses/gpl-3.0.html
 */
defined('_JEXEC') or die('Restricted access');
?>
<div id="hikashop_product_top_part" class="hikashop_product_top_part">
  <h1>
    <span id="hikashop_product_name_main" class="hikashop_product_name_main">
      <?php
      if (hikashop_getCID('product_id')!=$this->element->product_id && isset ($this->element->main->product_name))
        echo $this->element->main->product_name;
      else
        echo $this->element->product_name;
      ?>
    </span>
    <?php if ($this->config->get('show_code')) { ?>
    <span id="hikashop_product_code_main" class="hikashop_product_code_main">
      <?php
      echo $this->element->product_code;
      ?>
    </span>
    <?php } ?>
  </h1>
  <?php
  $pluginsClass = hikashop_get('class.plugins');
  $plugin = $pluginsClass->getByName('content', 'hikashopsocial');
  if (@ $plugin->published || @ $plugin->enabled) {
    echo '{hikashop_social}';
  }
  ?>
</div>
<div id="hikashop_product_left_part" class="hikashop_product_left_part">
  <?php
  $this->row = & $this->element;
  $this->setLayout('show_block_img');
  echo $this->loadTemplate();
  ?>
</div>
<div id="hikashop_product_right_part" class="hikashop_product_right_part">
  <div id="hikashop_product_vote_mini" class="hikashop_product_vote_mini">
    <?php
    if($this->params->get('show_vote_product')){
      $js = '';
      $params = null;
      $this->params->set('vote_type','product');
      if(isset($this->element->main)){
        $product_id = $this->element->main->product_id;
      }else{
        $product_id = $this->element->product_id;
      }
      $this->params->set('product_id',$product_id);
      echo hikashop_getLayout('vote', 'mini', $this->params, $js);
    }
    ?>
  </div>
  <span id="hikashop_product_price_main" class="hikashop_product_price_main">
    <?php
    if ($this->params->get('show_price')) {
      $this->row = & $this->element;
      $this->setLayout('listing_price');
      echo $this->loadTemplate();
    }
    ?>
  </span>
  <?php
    $this->setLayout('show_block_dimensions');
    echo $this->loadTemplate();
  ?><br />
  <?php
  $this->setLayout('show_block_charasteristic');
  echo $this->loadTemplate();
  ?>
  <br />
  <?php
  $form = '';
  if (!$this->config->get('ajax_add_to_cart', 1)) {
    $form = ',\'hikashop_product_form\'';
  }
  if (hikashop_level(1) && !empty ($this->element->options)) {
  ?>
    <div id="hikashop_product_options" class="hikashop_product_options">
      <?php
      $this->setLayout('option');
      echo $this->loadTemplate();
      ?>
    </div>
    <br />
    <?php
    $form = ',\'hikashop_product_form\'';
    if ($this->config->get('redirect_url_after_add_cart', 'stay_if_cart') == 'ask_user') {
    ?>
      <input type="hidden" name="popup" value="1"/>
    <?php
    }
  }
  if (!$this->params->get('catalogue') && ($this->config->get('display_add_to_cart_for_free_products') || !empty ($this->element->prices))) {
    if (!empty ($this->itemFields)) {
      $form = ',\'hikashop_product_form\'';
      if ($this->config->get('redirect_url_after_add_cart', 'stay_if_cart') == 'ask_user') {
      ?>
        <input type="hidden" name="popup" value="1"/>
      <?php
      }
      $this->setLayout('show_block_custom_item');
      echo $this->loadTemplate();
    }
  }
  $this->formName = $form;
  if($this->params->get('show_price')){ ?>
    <span id="hikashop_product_price_with_options_main" class="hikashop_product_price_with_options_main">
    </span>
  <?php } ?>
  <div id="hikashop_product_quantity_main" class="hikashop_product_quantity_main">
    <?php
    $this->row = & $this->element;
    $this->ajax = 'if(hikashopCheckChangeForm(\'item\',\'hikashop_product_form\')){ return hikashopModifyQuantity(\'' . $this->row->product_id . '\',field,1' . $form . '); } else { return false; }';
    $this->setLayout('quantity');
    echo $this->loadTemplate();
    ?>
  </div>
  <div id="hikashop_product_contact_main" class="hikashop_product_contact_main">
    <?php
    $contact = $this->config->get('product_contact',0);
    if (hikashop_level(1) && ($contact == 2 || ($contact == 1 && !empty ($this->element->product_contact)))) {
      $empty = '';
      $params = new JParameter($empty);
      echo $this->cart->displayButton(JText :: _('CONTACT_US_FOR_INFO'), 'contact_us', $params, hikashop_completeLink('product&task=contact&cid=' . $this->row->product_id), 'window.location=\'' . hikashop_completeLink('product&task=contact&cid=' . $this->row->product_id) . '\';return false;');
    }
    ?>
  </div>
  <?php
  if(!empty($this->fields)){
    $this->setLayout('show_block_custom_main');
    echo $this->loadTemplate();
  }
  ?>
  <span id="hikashop_product_id_main" class="hikashop_product_id_main">
    <input type="hidden" name="product_id" value="<?php echo $this->element->product_id; ?>" />
  </span>
</div>
<div id="hikashop_product_bottom_part" class="hikashop_product_bottom_part">  
  <div id="hikashop_product_description_main" class="hikashop_product_description_main">
    <?php
    echo JHTML::_('content.prepare',preg_replace('#<hr *id="system-readmore" */>#i','',$this->element->product_description));
    ?>
  </div>
  <span id="hikashop_product_url_main" class="hikashop_product_url_main">
    <?php
    if (!empty ($this->element->product_url)) {
      echo JText :: sprintf('MANUFACTURER_URL', '<a href="' . $this->element->product_url . '" target="_blank">' . $this->element->product_url . '</a>');
    }
    ?>
  </span>
  <?php
  $this->setLayout('show_block_product_files');
  echo $this->loadTemplate();
  ?>
  <div id="hikashop_product_vote_listing" class="hikashop_product_vote_listing">
    <?php
    if($this->params->get('show_vote_product')){
      $js = '';
      $params = null;  //Params already existing in the previous getLayout('vote', ...)
      echo hikashop_getLayout('vote', 'listing', $params, $js);
      ?>
  </div>
  <div id="hikashop_product_vote_form" class="hikashop_product_vote_form">
      <?php
      $js = '';
      $params = null;
      echo hikashop_getLayout('vote', 'form', $params, $js);
    }
    ?>
  </div>
  
      </div>
</div>

.
You just have to move the part:
[code]
  <?php
  if(!empty($this->fields)){
    $this->setLayout('show_block_custom_main');
    echo $this->loadTemplate();
  }
  ?>

  <div id="hikashop_product_description_main" class="hikashop_product_description_main">
    <?php
    echo JHTML::_('content.prepare',preg_replace('#<hr *id="system-readmore" */>#i','',$this->element->product_description));
    ?>
  </div>