Go to the environment tree item under the rendertarget item in the Render Options List on the Settings tab, and change the default “texture environment” to “daylight”. You can then control the sun position. from the sliders.
Turbidity
The Turbidity can be used to adjust the sharpness of the sunlights and shadows. A low value creates sharp shadows (like on a sunny day) and a higher value diffuses the shadows similarly to a cloudy day.