Regarding Jumps, Heights, and Scripting

Hello. After a long time of no activity, I have forgotten a lot about programming. Now. I have a 2D sprite character that the player will control. This character has a simple 2D box collider and a rigidbody. I have figured out how to make the little guy move use vectors, and have gotten him to go up. What I want to know is how to make him stop going up after reaching a specific height (say, 2 meters above where he started), and come back down. Here is the script I have thus far. A little help in collision detecting would be useful as well. Thanks in advance.

 public var speed : int = 5;
 public var jumpSpeed : int = 10;
 public var gravity : int = 10;
 
 function Update () {
 
     rigidbody2D.AddForce (-Vector2.up * gravity);
 
     if (Input.GetAxis("Horizontal") > 0)
         transform.Translate (Vector2.right * speed * Time.deltaTime);
         
     if (Input.GetAxis("Horizontal") < 0)
         transform.Translate (-Vector2.right * speed * Time.deltaTime);
         
     if (Input.GetButton("Jump"))
         rigidbody2D.velocity = Vector2.up * jumpSpeed;
         
 }