I haven't looked into Tienda, but if this is like with Virtuemart, it's probably a PHP file, or several, that creates that email. You'll have to edit that yourself.
Gavick doesn't answer your question as this is way beyond support for template problems. You might ask this question in the Tienda forum - if that exists.
Cheers,
Tom
P.S. To Gavick: It might be helpful if Gavick would answer these hanging posts likewise. At least the member knows immediately that there's nothing to wait for here. Just a suggestion