[You can do it, but there's no direct way to do so.]
|Revise your message|
| 1. Copy your message and revise it.|
2. Copy the new text and/or code.
3. Paste the revised info into a new message.
4. If it works out right, delete (Remove) the original message.
|Remove Message In Blogger Help Group:|
| 1. Click on "more options" in the upper right corner of your own message.|
2. Click on "Remove" in the list of options in blue text.
3. Click on "Yes, remove it now".
4. Click the "Confirm" button.
If it feels like you're telling it to do the above 3 times at least, welcome to the club!