If you have started a thread....you can go back to your original post and click the edit button at the bottom of the post. Then click ADVANCED. In that screen you can edit or update your title as well as the original posting.
To bump a thread is just to post something to it ... usually the word bump....to bring it back to the "top" of the current threads so people who may have missed it can see it.
Okay...I just went to a thread I started, clicked on Edit in the first post, clicked advanced, then changed the title. Then, if you save that, and then post a reply as a new post, it should bring it up to the top.
Nope, you are right. It updated the title once I opened the thread, but didn't change it on the list. I am now officially clueless. (It was unofficial previously.)