You can edit a post that you have already added by clicking on the "Edit" button that appears on it.The Edit funciton is set up to discourage people frome editing their post for the wrong reasons, so you can only edit it within 15 minutes of posting - leaving you a bit of time to correct spelling mistakes and so on.Note that you can only save changes if you describe the changes you have made in the Edit Notes box. Again, this is to discourage abuse of the facility.