XF 1.4 Move a message to one user to another user

Being new to XenForo I have a testuser account that I use to try out many of the XenForo features as a user. Is there a way to transfer the posting to a life account once I am happy with what I see?
I have been looking in the manual on merging of accounts (Users), but I can't seem to find it. Would someone be so kind to forward me a link in the area in the manual, I would find this? Do one of the users have to be deleted for this to work?