The fastest way to do this would be to reach full evil by killing a lot of innocents. To do this you need to turn safety off from the expressions menu, the lower left choice just after hitting RB, sometimes comes up on the shortcuts as down.
To reach fully good, your only real hope is the Temple of Light donations and quests. Raising to full good by donating to the Temple is a very long process and probably will make you want to break the game disc in half. Really if you are wanting to be full good, for your own sanity, rely on making good choices during the quests.