Bespoke code - where should I add it?

Hi,

I'd like to override the front-end display code of a table to reformat the content as a document and not a table.
Is there somewhere I can put this code?

E.g. currently:

<div class="item_fields">
<table class="table">

<tr>
<th><?php echo JText::_('COM_BOXLEAGUE_FORM_LBL_BOXLEAGUE_ID'); ?></th>
<td><?php echo $this->item->id; ?></td>
</tr>
<tr>
<th><?php echo JText::_('COM_BOXLEAGUE_FORM_LBL_BOXLEAGUE_BL_NAME'); ?></th>
<td><?php echo $this->item->bl_name; ?></td>
</tr>
</table>
</div>

However I would like something like this:

<div class="item_fields">
<h1><?php echo $this->item->bl_name; ?></h1>
</div>