Hi,
You can only do this change through PHP file.
Open this PHP file (for product details page layout):
/templates/YOUR_TEMPLATE/html/com_virtuemat/productdetails/default.php
(default.php or flexv2.php depends on which layout you are using for product details page)
And look for this line:
<div class="FlexibleProductDetailProductName"><?php echo $this->product->product_name ?></div>
and replace it with:
<h1 class="FlexibleProductDetailProductName"><?php echo $this->product->product_name ?></h1>
(you may change the class name to re-define your own CSS rules if you would like)
Regards.
Support & Development