Ability to merge contacts within one account?

I’m using the NXT version of CS and am looking to merge two contacts listed under one account. 

Occasionally our clients will update their email addresses, so we’ll have two separate contacts (one current and one that’s outdated) that represent the same person. We don’t want to just delete the old one and lose all of the activities they were part of. 

Ex. customer@abc.com changed their email address to customer@xyz.com, want merge the two so that @xyz.com will be associated with all historical activities @abc.com was part of, and then be able to delete @abc.com

Is there a way to accomplish this in NXT?