The best way as mentioned above is using the Edit Environment panel. Shadows are influenced by the balance between Ambience color, Sun color and Brightness. What I do is to drop the ambience way down then adjust the Sun and Brightness to get the lighting I like. Then bring the ambience back up to lighten up the shadows. Tip: Holding down the Shift key while tweaking the knobs allows you to adjust all three at the same time.
