How to change one's sleeping pattern in just one day?

You can't. Most people can't 'phase adjust' more than 15-30 minutes per night. When possible, give yourself enough time to gradually & methodically shift your sleep pattern. In cases where you have to adjust quickly (travel for work, etc), medications can be immensely helpful, both to initiate sleep & to promote wakefulness. Admittedly, this is an unnatural solution to an unnatural problem. Talk to you doc.