Can I abdicate?

[Notna07]

My old king became incapable and is now sharing power with his son. Is there a button to just start playing as the heir or do I have to get rid of the poor old man?

[Doc Dreamist]

Few ways to abdicate:
1. Invoke tyranny war and surrender. This can have some negative side effects so read surrender terms beforehand.
2. Suicide. Also some had side effects.
3. Stress. If you really stress out your character you can get an event to abdicate.

There are probably more but those are the few j can remember off the cuff.