D.F.
My son was about the same age when I took him from the crib to the "big boy" bed, and all went well with a couple of steps. First, does he sleep in that room now with the crib in it? If no, I would say put his crib in there, read a book to him in the "big boy" bed, and then move him into the crib to nap do this for a few days, then move to having him take naps in the bed, play in the room with him to make him comfortable, but mainly whatever you do you need to make the room a safe and happy place for him and not one of forcing (for a lack of a better word) to sleep in the bed. We used to have a parade every night when it was time to go to bed (just being in a line one behind the other and humming) we would walk all around the house (the parade route), that way it was fun every night and my son went to bed on a happy note and had happy dreams.