mouse control with slower rotation

hi, i need help with completion of my player control script. i try change rotation control from keycode to mouse but now i dont know how make rotation slowly. here is my script:

#pragma strict

var speed = 0f;
var score = 0;
var maxspeed : float;
var acceleration : float;
var SpawnPos : Vector3;
static var Plife = 3f;
var animator: Animator;
var mousepos : Vector3;

function Start () {	
}

function Update () {

    var objectPos = Camera.main.WorldToScreenPoint(transform.position);
    var mousepos = Input.mousePosition - objectPos; 
    transform.rotation = Quaternion.Euler (Vector3(0,0,Mathf.Atan2 (mousepos.y,mousepos.x)* Mathf.Rad2Deg)); 
	transform.Rotate(Vector3(0,0,-90));	//i need to make this rotate slower.
	
	if(Plife <= 0f){
		transform.position = SpawnPos;
		Plife = 3f;
		score -= 1;
		speed = 0f;
		NewPlShooting.spawnDelay = 0.1f;
	}
	
    GUILayerScript.speed = speed;
    GUILayerScript.life = Plife;
    GUILayerScript.Pscore = score;
    GUILayerScript.position = transform.position;
    NewPlShooting.Pspeed = speed / 40;
    ParticleControler.speed = speed;
    
    if(Input.GetKey(KeyCode.C)) {
		if(GetComponent(CircleCollider2D).enabled == false) {
			GetComponent(CircleCollider2D).enabled = true;
		}
		else if(GetComponent(CircleCollider2D).enabled == true) {
			GetComponent(CircleCollider2D).enabled = false;
		}
	}
}

function FixedUpdate() {
	if(Input.GetKey(KeyCode.W)) {
		rigidbody2D.velocity = transform.up * speed * Time.deltaTime;
		animator.SetBool("stop", false);
		animator.SetBool("stop2", false);
		if(speed < maxspeed) {
			speed += acceleration;
		}
	}	
	else if(Input.GetKey(KeyCode.S)) {
		rigidbody2D.velocity = transform.up * speed * Time.deltaTime;
		if(speed > -400) {
			speed -= acceleration * 2;
		}
	}
	else {		
		rigidbody2D.velocity = transform.up * speed * Time.deltaTime;
		animator.SetBool("stop", true);
		animator.SetBool("stop2", true);
		if(speed > 0) {	
			speed -= 1f;
		}
		else if(speed < 0) {
			speed += 1f;
		}
	}
}

function OnCollisionEnter2D(col : Collision2D){
	if (col.gameObject.tag == "bullet1") {	
		Plife -= 1f;
	}
}

thx for help.

Hi

var mousepos = Input.mousePosition/SMOOTH - objectPos;

try smooth = 0.5 and the rotation by mousePos will be slowly, you can use smooth to make an sensitivity option.

Hope it will help