Once you have been a member for a while you can edit your own posts - but only for 10 minutes after making the post. You cannot delete posts.
Forum moderators can edit or delete posts but we are generally reluctant to delete posts unless they contain spam, offensive or sensitive data that should not have been posted publicly. If you have made a post that needs editing or deleting for some reason like that, then click the 'Report' link at the bottom left of the post and explain your request. A moderator will assess the request and act (or not) accordingly.