Just recently went from sleep 2am-11am to 11.30 to 6.30
1. Make sure your sleep quality is actually good, otherwise you'll always want to keep sleep longer.
2. Make it consistent, sleep the same time everyday and wake up the same time. You won't need an alarm 3 weeks later.
3. Get straight out of bed, no checking messages or anything. Jump straight out so your body knows that 6am means wake up time.
Extra tips would be:
only use your bed for sleeping, if you sit in bed or lay in bed at other times, your body will get used to that and keep you awake.
turn your lights off 30 mins before you sleep and I would say don't use your phone within the last hour of sleeping but no one will do that, so just turn your brightness to the absolute lowest and even download an app that makes it even darker. Just prepare your body for it to know that you're about to sleep and when you wake up, prepare it to know it needs to wake up, open the window, feel the breeze, have a cold shower, turn the lights on, do a quick stretch.