Also, when you're in the animation palette, you can click on the little triangle next to the arm (or any other part) and select the specific action you want to change (xtrans, y rotate, bend, side-to-side, etc.) and just delete (or change) that motion. That way you can preserve other motions of the arm (or other part) that you want to keep. The animation palette is really quite a powerful, flexible, and easy to use tool.