Hi, I realised something after playing a couple of generations.....how do you decide/pick your heir? Is there a pre-requisite of which family member will be the heir? And after that guy is selected, can you change it? i.e choose someone else to be the heir.

I was searching through the menu buttons etc, cannot see anything that I can select to change the heir. I guess the only thing is to send that poor guy on a suicide mission....wow, what happens after that and the new heir is still not the guy I want? I'll be on endless suicide missions. There must be a way to pick my heir right?