Thread: I really need to change my sleep schedule, but what's the best way to do that?

My sleep schedule right now is that I go to sleep at around 4 AM in the morning, and then get up at 12 PM, sometimes slightly later.
This is obviously not a very ideal schedule, at least not while studying, like I do, so I really need to change this schedule - but what's the best way to do that with minimal harmful effects?
Yesterday I felt kind of tired because I had not slept very well that night, so last night I figured that I should probably fall asleep right away, since I felt so unrested, and I made a point of getting up at 8 AM the next morning - and I did fall asleep for about an hour shortly before midnight, but then woke up because I really needed to go to the bathroom, and then I couldn't fall asleep again.
I lay awake until like 6 AM, and at that point I no longer cared about waking up early, because I was so tired that I seriously felt like I was drunk - it would have been risky for me to walk to school at that point, since I would probably trip and fall somewhere, that's how tired I was, and I also shivered and had a terrible blood circulation, so the thought of taking a ten-minute walk to school at 22° F in the morning felt pretty disgusting as well.
Thankfully I did fall asleep shortly after that, and now it's 2:42 PM and I feel reasonably rested - but I cannot go on like this, and I really need to change my sleep routines.
Do you have any advice?