I've made this massive adjustment in my sleep schedule on several occassions. I find the best strategy is to just "jet lag" it. Rather than gradually adjusting from waking up in late morning or early afternoon to 6:00 AM, I just force myself out of bed at 6:00 AM in one shot.
If you need to, set two alarms, one across the room from where you sleep. It's so important to physically get up, because I find that if I lay around at all I fall back asleep.
On that first day, I'll also allow a short power nap around late afternoon to help me along. It's a groggy strategy, but it works for me.
Have fun.
