Opencart product page layout not modifying

I am using Opencart 2.1.0.1 and default template. And i want to update Product layout. When i go to following path catalog/view/theme/default/template/product and update product.tpl. No effect showing on front end. If i remove all code or comment all code on product.tpl no effect showing on product page. YEs but when i rename product.tpl it will not showing. Please guide me how i can update product page.

Thanks

Have you gone into BO/extensions/modifications and clicked the refresh button ??

Also clear your caches: http://forum.opencart.com/viewtopic.php?t=69439