Hi, I am 21 week pregnant. The baby's head is up and not down yet. Will he change position? Anything to do to help? I want natural birth.

Position. Fetal presenting part is very variable early on in pregnancy. In a women having her first child the fetus will come to it's final position by around 32 weeks. In a women who has had children before this may occur later on. If the baby is breech later on options like version can be discussed, but it is too early to concern yourself with the fetal position.
Don't worry. Most babies will turn head down in the third trimester.