This document explains how to modify an existing email template in Salesforce. Note: this is not to be confused with SOAPBOX Mailer emails.
1) Go to your user name in the upper left of the Salesforce application (1)
2) Select 'My Settings' (2)
3) Choose 'Email' from the list that appears on the left of the screen (3)
4) Select 'Email Templates' from the resulting list (4)
5) Select your team folder from the 'Folder' dropdown (5 & 6)
6) Click on the 'Email Template Name' that you wish to edit (8)
7) The email template is now available to edit. Remember to update both the HTML and Text versions. (9 & 10)
8) Save your document
9) Be sure to sent a test to yourself to make sure the changes are correct.