Moving Domains From One account to another

I have three domains that I manage under one email account (Login A) and one domain I manage under another email account (Login B). I'm trying to consolidate everything under Login B that currently has the one domain. How can I go about moving the three domains to Login B so I can close down Login A? Thanks!

Update - I did figure out how to share permissions, but I want to be able to switch the account that is the owner.