When should I change my baby's crib into toddler's bed?

About Hyerim
Born: Minot, North Dakota
Current: Minot, North Dakota
Birth: July 13
On since: Feb 3, 2014
Hello, I'm a mother of a 15-month-old boy and am pregnant at the moment (probably into 8-9 weeks). Can't wait to go to the hospital and hear his/her heartbeat.