Hi there, as an admin, you can edit all posts. All you have to do is go to the main post(the first post in a topic) and click on more > edit you will see that you can also change the topic title there.
Titles and meta tags are like "keys" that search engines(like google) use to find webpages. with nabble, you can set specific meta tags for each topic to make it more "friendly" with search engines
:) Helper