Can you change your circadian rhythm?

Yes. The common ingredients for changing your circadian or "daily" rhythm is about two key things: light and melatonin. There are two types of disorders regarding circadian rhythm, delayed sleep phase and advanced sleep phase. In delayed sleep phase disorder, you go to bed late and wake up late. The corrective treatment is to have light exposure when you wake up and take melatonin before bed. Suerte.
Yes. Circadian rhythms are both set by internal molecular clocks as well as responsive to environmental forces, the most powerful being light in the case of the sleep-wake cycle. This is one reason why some peoples normal clock may get delayed. Some individuals are more sensitive to adjustments and others more difficult. Be careful to adjust your rhythm on your own. Get advice from a sleep doctor.