At the moment, you're only able to create and edit email response templates when you click Reply next to an active customer comment (it's an annoying quirk - we know - this will be fixed up when we release our new Messaging Portal...watch this space!)
In the meantime, here's what to do:
Step 1: Click on the Ratings tab along the top toolbar
Step 2: Click the Reply button next to any active comment (don't worry, you won't need to send a reply unless you want to!)
Step 3: Choose the template you would like to edit from the list to the left
Step 4: Edit the subject and email message as needed
Step 5: Click Update Template button down the bottom
Step 6: At this point, you can either send the reply or click cancel (the template updates will be saved!)
Step 7: That's it!