How do I change the way I log in?

Hello everyone, I have been playing Candy Crush Saga for years. I log in via my Facebook account. Now I would like to change this and be able to log in via a king account or via email with a password. I've tried everything but I don't see that option anywhere? Is there a way to change this so that my game and levels are preserved because after all these years there are a lot of them that I absolutely don't want to lose, who can help me with this? Can you convert this to king? Would love to hear tips