Merging two thread into one - how to edit title?

[TeroRe]

Thread 1, title xxx

Thread 2, title yyy

I merge threads to together. With Inline replies (I think) there is no way to edit title from the thread what is merged into the another?

Currently there is no title field elsewhere than in the first post but when you go to the Recentpostpage (for example) you can see that replies uses sometimes the old title (depending what comment people are replying to).

I want that each and every comment has same title than the topic title actually is.

How to do this?

[NicoleC]

If you merge a thread with subject line "ABC" into a thread entitled "123", the new thread title will be "123" so you would need to manually edit the replies of "ABC" in order to change the subject lines for them. Any new replies to that thread will adopt the "123" subject line automatically. So, it's a matter of changing the "old" subject lines to match. 

[TeroRe]

Sorry, I didnt explain proberly. There isnt title field in the comments any more. Just like here Atlas, I cant see the title field. Where to edit it or how to?