This isn't currently clear and the instructions both aren't very obvious and are buried in "Terminating Instances", which doesn't seem like related documentation.
Original Report
Only the person that created our account can manage the instance, even though we've made other people admins in the project. So, for example, we'd like all of our project admins to be able to click on this instance and invite new users. We can't figure out how to give anyone else permissions to invite new users or see our other instance settings.