What is the most effective way to kill my wife?

I don't like my current wife so I need to get rid of her. What would be the most effective way to replace her? What other ways are there?

There are three main ways to get rid of your wife:

1. Assassinate her. If this fails, your wife may be lethally annoyed at you.
2. Start a plot against her, from the Intrigue screen. This plot will always be available when you are married. Again, if your wife finds out (due to one of your fellow plotters spilling the beans), your wife may let her displeasure be known in similarly-lethal ways.
3. If you're Catholic, you can ask the Pope for a divorce. It costs 50 piety, and you'll need the Pope to like you, but otherwise it has no drawbacks; you can re-marry immediately after a divorce.