Darkness can only be eliminated when there is light (like a lamp, or sunlight). In the same way, negative things can only be replaced by positive things. Remember that regardless of what is happening to us externally, or how bad things appear in our mind, we always have the choice to speak and see things positively.
I know this is harder to do when youre in midst of heated emotions, but Im a big believer that there is something to be learned from every situation we encounter. Look for the lesson. Find something about the situation that youve gained, whether its a material possession or an understanding or a personal growth. Find the light so you can uncover the darkness of your mind.