I found it. You go to the left side of your original post, click on your user name. It opens a screen showing a link to your thread. Click that. Go to the top of that edit page, as it has the title. At the top there are more options, and click the "more tools" (little wrench) button next to "unwatch thread" button. In there you will get a drop down with Edit Title.
Update: If you are the OP, there is a little wrench at the top whenever you open the post. The edit button at the bottom will not let you do it.
I guess you can unwatch you're own thread if you've said some thing controversial or it contains to many UK fans. LOL.