Located under the SMTP configuration settings, the options for customizing email templates can be found.
The first option is to choose from the dropdown what email language you wish to customize. This dropdown contains all the languages you have set on your exchange.
Here you can see how by changing the language to French, the Account Upgraded email I am now editing is just for the French version of this email
After selecting the email's language, from the second dropdown choose what type of email template you wish to edit. There is a wide variety of these emails so you can use the search function to assist you.
Examples of some of these templates:
Among many others
With your email type chosen, you will see the default title and email content. These can both be easily changed, the title via the top text field.
The email content uses HTML and can be edited as much or as little as you want. Once you are happy with all your changes, click the green 'Save' button to apply them.
In addition to customizing emails, also on this page, an auditor email account can be set. This account will receive copies of all important emails sent out by exchange. Simply enter the desired email into the text field and save.