From Hero-Deity to a Demigod? How should it be done?

[Jon_Dahl]

If a hero-deity wishes to become a demigod, what steps should he or she take and how difficult should it be?

To be more precise, I'd like to advance Nazarn from hero-deity status to demigod status in my game (I'm the DM), but I'd like to do it by the book. I just don't which book...