There is a time window after you post a message that you can edit it. Not sure how long that window is, but it may be a couple of hours. You need to go to the account manager icon at the top of the page and then go to "my board posts" which should be listed as one of the options on the left part of the screen. Go to the post in question and there should be an "edit my post" option at the bottom. If it is there, then make your changes. It will then go to a moderated post and have to be reviewed by the Mod, whether you are moderated or not, and then will be made public.
If you don't see the edit option, and the post is active on the board, then you will need to send a PM to the Mod and ask that he take the post down. You can then rewrite.  (still not Mr. Fisher)