You probably don't have to lower it. What I did was place them on the roost every night for a few nights. They are creatures of habit so once they start sleeping up there they will continue even if you don't help them.
You need to have a water heater for sure. You don't necessarily have to have a heat lamp if you have proper ventilation and bedding.
Other things to do to help keep your chickens snug this winter include using straw as a bedding, using the 4" inch side of a 2x4 roosts. I also put a towel that...