How do I lower high potassium. Diet is not enough?

Hmmm. You don't say enough to indicate any particular answer. I wonder how you determined that you have high potassium. What exactly leads you to say "Diet is not enough", since diet is the only thing you are talking about?

Potassium and sodium are needed in balanced amounts. The sodium ion makes the cells hold water, and the potassium ion makes them dump water. Too much of either can make the heart fail. So you want to learn your subject completely before you attempt any heroic corrections.