well, to cleanse them:
sit down, calm your mind.
start at your red chakras and "light them up" by imagining them coming to life and spining in a clockwise direction. go all they way up to your crown chakra. when you do this make sure they pick up speed and fling all the icky black stuff to the ground to be cleansed.
here is a cool little quiz, that may not be right, but is fun to do that tells you abotu your chakras and how "active they are: http://www.eclecticenergies.com/chakras/chakratest.php