The breast is an amazing milk factory -- it will adjust to whatever schedule you put it on. The trick is to not make any sudden changes. If you are currently pumping during the day, try eliminating one pumping session every few days or so. You may find that your breasts get pretty full if you skip a pumping session, and if so, it helps to pump just enough to alleviate the pressure. Don't try to "empty" the breast, as that is the signal for the breast to make more milk rather than less. If you drop the daytime feedings too quickly (without this relieve-the-pressure pumping) you may set yourself up for a breast infection.

Many moms find they can just breastfeed at night and not during the day, while others find that their milk supply dwindles. One way to help keep your supply going is to get as many nursings in as you can when you are with your baby. Nurse your baby right before you leave him in the morning and again when you pick him up in the afternoon and then as often as he wishes when you are home. Nursing on weekends will help gear up the supply for another week.

Hope that helps!