How do you ask for a later bedtime?

Easy, first you have to prove you wont get tired if you stay up that late. Like on a weekend stay up till your desired bedtime and the next day get up before your parents, and when they comment on your early awakening say, "I don't know why, but it was so much easier to fall asleep last night." Then just convince them to let you stay up a half hour later, then gradually ask for another increase until your desired time.