First make sure that they have been in the coop and run long enough to consider it home. Then at first just let them out maybe an hour before dark.At first they may not all come out but the braver ones will and it won't be long before the others follow, and then its just a matter of watching them to see if they all go back in.When you first let them out don't be suprised if one or two of them get confused and can't find the door, it seems like every time I let a new group of chicks out there is always one that can't find the door and ends up running back and forth along side of the run.Just gently herd them back to the door and they will go in.As your flock gets better at going to bed by themselves you can increase the time you let them free range.
The only problem that might come up is the could start laying in the yard if their out all day,I don,t let my girls out till after noon when most have already layed.