To make climbing hills on your bike MUCH easier, do this:
Get a good pace going before you reach the hill
Sit back in your seat, try to keep a steady pace and when you feel your legs slow down, drop to a lower gear. Also, gently rock the bike side to side.
You don't want to lean forward, it will kill your knees. Its ok to stand every once in a while to get some more momentum, but it will wear you out faster on longer hills.