go to backend catalog->product->selectyourproduct->design->custom layout update and write below code .
<reference name="product.info">
<action method="setTemplate">yourTemplatePath/yourTemplate.phtml</action>
</reference>
go to backend catalog->product->selectyourproduct->design->custom layout update and write below code .
<reference name="product.info">
<action method="setTemplate">yourTemplatePath/yourTemplate.phtml</action>
</reference>