To change thread titles click edit under your post and then click more options. you should be able to change the title.
I tried that but didn't see any option like that in more options. It seems like you can't do that anymore. Clicking more options seems to only give you the extra option of uploading a file with the post. More "optionS" is a lie! :O Actually it also provide you the option to get email notifications about the thread. The unwatch option is already on the top right normally though.
