Moving Threads 
If you would like to move threads from one forum to another that are older than a certain date, or have been posted by a certain user, click on the Move link under the Threads section of the control panel. Once you have clicked on the link, the following screen will appear:

The first form on the page will allow you to move all threads from one forum to another that are older than a specified number of days.

The second form on this page will allow you to move all threads that have been posted by a specified user from one forum to another.

After selecting the options and pressing the button, you'll be taken to a confirmation screen, where you can either choose to move all applicable threads, or you can select the ones you would like to move.
Note:
Moving and pruning threads are both fairly server intensive.
User Contributed Notes: Moving Threads Add a Comment