Body Clock

I slept around 11:30 in the evening last night. I was very tired and sleepy. I really wished having a complete 8 hour sleep, however, I woke up 4 in the morning. I guess it was my body clock. My body clock is messed up, and I hate it.

I want to change my routine so that I can get to sleep at 11pm, and wake up at 8. How can I force my body clock to comply?