Promotions are obtainable at certain milestones after the completion of a specific task. There are currently four promotion levels and methods of being promoted further.
Basic - You start level 8 here.
Adept - This promotion can be purchased from Queen Yvonne for 100,000 gold coins. There is no level requirement to receive this promotion. Queen Yvonne is at the north-most part of the main city.
Elite/Master/Royal/Elder - This promotion is earned as the final reward from the Initiation Quest. You can find more information about this quest by asking Queen Yvonne for a promotion once you have been promoted to Adept. You must be level 600 to start this quest.
Surpreme/Arcane/Divine/Enlightened - The final promotion is earned as the final reward from the An Alternate Fate Quest.