How about shadow smoothing? In the atmo editor, light tab. But since the noise only happens on the figyres, my guess is it comes from the textures. Use some texture filtering in your renbder settings (33%) usually does the trick. To access texture filtering, you'll need to use your own render settings. If you don't know what to use as custom render settings, there is a Load button to load a Render settings file, simply load the Superior mode (for example), then you can access texture filtering by clicking on the Edit button next to Anti aliasing settings.