var bf : boolean = false;

var controller : CharacterController;  
  var oldHeight;  
  var newHeight: float;  
  var newPos;
  var bf : boolean = false;  

  function Start () {  
  controller = GetComponent(CharacterController);  
  oldHeight = controller.height;  
  }  

function Update() {     
newPos = new Vector3(transform.position.x, transform.position.y + 0.7f, transform.position.z);
            if (Input.GetKey(KeyCode.LeftControl)) {
                controller.height = newHeight;
                bf = true;
            } else {
            if (Input.GetKeyUp (KeyCode.LeftControl) && !Physics.Raycast (transform.position, Vector2.up)) {
                controller.height = oldHeight;
                transform.position = newPos;
                bf = false;
            } else {
            if (bf == true && !Physics.Raycast (transform.position, Vector2.up)) {
            controller.height = oldHeight;
                transform.position = newPos;
                bf = false;
            }
            }
            }
}