WWII, here are the instructions from the yuku support forums ~ Sooz
To merge two or more topics into a single topic, you need to be on the topic listing (forum) page.
Check the boxes beside each of the topics that you wish to merge and select Merge Topics from the topic tools drop down menu.
You will be asked to choose a new topic title for the newly merged topics
The original date is checked by default, it will keep the replies in order of the dates they were posted.
Choose which one of the lead posts will become the new lead in the merged topic. This does not have to be the oldest post.
Click submit to merge the topics.