Help me change the code to work with Physics 2D

Could anyone help me to change this code to work with Physics 2D because all of my game works with Physics 2D and this code doesn't but I'm not sure how to do it. It works fine with Physics but it doesn't work with Phyisics 2D and thats what I want.

Code:

 private var ray : Ray;
 private var rayCastHit : RaycastHit;
 
 function Update()
 {
 
     if(Input.GetMouseButton(0))
     {
         ray = Camera.main.ScreenPointToRay (Input.mousePosition);
         
         if (Physics.Raycast (ray, rayCastHit))
         {
             transform.position.y = rayCastHit.point.y;
         }
     }
 }