No, you cannot "unbank" them. They are in your next use year. For example, if you have an April use year and bank your 2009 points, they will become April 2010 points, which are good for stays 4/1/10 to 3/31/11. You can however, borrow your actual 2010 points into 2009 if you want to stay before 4/1/10 (you can't borrow the banked).
Your banking deadline is 4 months before the end of your use year. For April, it is November 30.