How can I change my sleep habits? I am awake during the night and sleep during the day?

Slow changes. You'll need to slowly change the times you are awake and asleep by shifting things by an hour or so a week until you shift back to a normal day-night pattern. Using natural sleep aids like l-theanine and magnesium to help you sleep during night hours will help your body calm down and allow this change. Check local health food store for help with supplements.