Canned Responses is an excellent lab, but the interface is a little clunky. Use this tip to easily edit your canned responses as a draft email.
For an easy way to edit a canned response, search for it's subject and you'll see it as a "Draft". Click on the email and a draft email will open, which you can edit and save. Hey presto!
You can also use "Discard" as a quick way to delete any canned responses you no longer need. So, it's not a good idea to press discard to exit the canned response draft - as it will delete it!
PS: You'll know it's a canned response because it's a "draft" that you can't see in your Drafts label. However, because it is an email you can find, why not create a "label" called Canned Responses and keep track of them that way.