Along with the preview feature before posting your message you can also edit your own post within 6 hours after it has been submitted to the bulletin board. You must be a registered member and logged on in order to have this feature available.
To edit your own post you would:
Click on your own message. In the upper right corner you will see an "edit" button next to the "reply" button. Press that button and it will bring up your message so that you can edit it. You again will have the preview options available to you as normal.