XF 1.4 Merge Multiple Users

A user has managed to create 10 accounts so that he can keep liking his own posts. I want to merge him into one account so that all of his posts are also named as the same username. then temporarily ban that one user for a duration of time.

How can I do that?
he has like 10 accounts. is there a way to quickly merge all under one user? i know its crazy but just asking if it can be done.