How do i change my sleeping time as its so screwed up now?

my sleeping time has never had been this screwed up!! for the past 1 week i've been sleeping around 6am to 7am and i usually get up at 11am to 2pm hmmmm. How to fix this problem???? as i dun get sleepy before 5am. hahahaha this is a real mess for me as m starting my work at 8.30am next monday.