I know you can change the forum thread title but where it says 'most recent post thing' I want the changed title to be there. How to do that?

It's either before a time limit or before someone posts, I don't remember which, you double click next to the title when you're in the board that has your thread. Also, you can go to thread tools and change the thread name there.

However, it's either after a certain number of post or after a certain amount of time has elapsed that you'll lose that ability unless you're a moderator of that board, and you'll need someone who moderates the board that has your thread to change it for you.