MDC: Before tampering with the ambient setting, you should check first why your models are too bright. A typical reason is that your level does not contain any light sources. In such a case not only your models, but your whole level won't look very good.

If you've placed light sources, but your models don't get lit by them, the usual reason is a displacement of your models. Open them in MED and make sure that their origin is in their center, and not outside the model or below their feet.