Hi,
If you want to edit an email sent by HikaShop there are several ways you can do it based on what you want to change.
If you want to change (or add to) the texts of the emails, the best is to do it with translation overrides, like the rest of the HikaShop interface:
www.hikashop.com/download/languages.html#modify
Otherwise, you can go in the menu System>Emails.
There, you can the emails sent by HikaShop and modify the template (the look / style), the HTML, and the preload (where the data is loaded for the tags used in the HTML version).
Note that you have a preview button there to check on the result.