Transform.position can't be changed smoothly.

Hello UnityAnswers, I have a problem. Not sure if small or huge tho! I have a code that allows an object to change it's position.x when you swipe to a direction. The problem that i have here is, I can't make it work to go from position.x = 0 to position.x = 4 smoothly. For example, when you swipe right, "Player" instantly goes to position.x = 4. I tried the code : this.transform.position.x = 4 * Time.deltaTime * 2; But nothing happens. Here is my full code written in JS.

 #pragma strict
 
 var firstPressPos : Vector2;
 var currentSwipe : Vector2;
 var current_pos : int;
 var speed : int;
 var can_speed : boolean;
 
 function Start () {
     current_pos = 2;
     speed = 3;
     speed_up();
 }
 
 function Update () {
     this.transform.position.z = this.transform.position.z + speed * Time.deltaTime * 2;
 
 
     if (Input.GetMouseButtonDown(0))
     {
         firstPressPos = Input.mousePosition;
     }
     if (Input.GetMouseButtonUp(0))
     {
         currentSwipe = Input.mousePosition - firstPressPos;
 
         if (currentSwipe[0] + 150 > 0)
         {   
             if(current_pos == 3){
                 return;
             }if(current_pos == 2){
                 this.transform.position.x = 4;
                 current_pos = 3;}
             if(current_pos == 1){
                 this.transform.position.x = 0;
                 current_pos = 2;}
         }
 
         if (currentSwipe[0] + 150 < 0)
         {   
             if(current_pos == 1){
                 return;
             }
             if(current_pos == 2){
                 this.transform.position.x = -4;
                 current_pos = 1;}
             if(current_pos == 3){
                 this.transform.position.x = 0;
                 current_pos = 2;}
         }
         }
     }
 
 function speed_up(){
     for(var i = 0; i  < 10; i++){
         yield WaitForSeconds (10);
         if(speed < 21){
             speed = speed + 6 ;
             InvokeRepeating("speed_up", 0, 2);
             can_speed = false;}else{return;}
     }
 }

Thanks for your time!