[{"id":1,"name":"Check","balance":1,"tokens":2,"energy":2,"ownerid":623465,"users":[{"cid":1285931,"uid":0,"level":3},{"cid":3272234,"uid":631,"level":1}]},{"id":2,"name":"Check2","balance":5,"tokens":12,"energy":51,"ownerid":171412,"users":[{"cid":1874345,"uid":543,"level":3},{"cid":2434512,"uid":212,"level":1}]}]

db.collection.update({"users.uid":543},{"$set":{"users.$.level":2}})