Character Zoom in and out

Hi,

Thank you for reading this thread. I am a very new student learning Unity 3d and I am having a hard time trying to implement zoom in and out on an object using mouse scroll wheel. The following is the object I am currently building and when I click PLAY, it gives me first-person view from the object,

https://docs.google.com/file/d/0B0dIErUqAOTnTHVWYmZfbldWSDQ/edit?usp=sharing

According to what I know, in inspector, I have to modified Mouse Look in bottom right side of the picture because it allows the mouse to control the view from the object. I have implemented the code (the codes between "Problematic Codes start here" and "Problematic Codes ends here")

 using UnityEngine;
 using System.Collections;
 
 /// MouseLook rotates the transform based on the mouse delta.
 /// Minimum and Maximum values can be used to constrain the possible rotation
 
 /// To make an FPS style character:
 /// - Create a capsule.
 /// - Add the MouseLook script to the capsule.
 ///   -> Set the mouse look to use LookX. (You want to only turn character but not tilt it)
 /// - Add FPSInputController script to the capsule
 ///   -> A CharacterMotor and a CharacterController component will be automatically added.
 
 /// - Create a camera. Make the camera a child of the capsule. Reset it's transform.
 /// - Add a MouseLook script to the camera.
 ///   -> Set the mouse look to use LookY. (You want the camera to tilt up and down like a head. The character already turns.)
 [AddComponentMenu("Camera-Control/Mouse Look")]
 public class MouseLook : MonoBehaviour {
 
     public enum RotationAxes { MouseXAndY = 0, MouseX = 1, MouseY = 2 }
     public RotationAxes axes = RotationAxes.MouseXAndY;
     public float sensitivityX = 15F;
     public float sensitivityY = 15F;
 
     public float minimumX = -360F;
     public float maximumX = 360F;
 
     public float minimumY = -60F;
     public float maximumY = 60F;
 
     float rotationY = 0F;
     
     // Mouse Scroll Zoom in and out
     public int zoomLevelSelected = 0;
     public float[] ZoomLevels = new float[] { 60, 40, 20 };
     
     float cameraDistanceMax = 20f;
     float cameraDistanceMin = 5f;
     float cameraDistance = 10f;
     float scrollSpeed = 0.5f;
     
     void Update (){
         int zoomChange = 0;
         
         if (axes == RotationAxes.MouseXAndY){
             float rotationX = transform.localEulerAngles.y + Input.GetAxis("Mouse X") * sensitivityX;
             rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
             rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);
             transform.localEulerAngles = new Vector3(-rotationY, rotationX, 0);
         }else if (axes == RotationAxes.MouseX){
             transform.Rotate(0, Input.GetAxis("Mouse X") * sensitivityX, 0);
             
             //Problematic Code starts here.
         }else if(Input.GetAxis("Mouse ScrollWheel") < 0){
             zoomChange = +1;
         }else if(Input.GetAxis("Mouse ScrollWheel") > 0){
             zoomChange = -1;
         }else if(zoomChange != 0){
             zoomLevelSelected = Mathf.Clamp(zoomLevelSelected + zoomChange, 0, ZoomLevels.Length - 1);
             camera.fieldOfView = ZoomLevels[zoomLevelSelected];
             //Problematic Code ends here.
             
         }else{
             rotationY += Input.GetAxis("Mouse Y") * sensitivityY;
             rotationY = Mathf.Clamp (rotationY, minimumY, maximumY);
             transform.localEulerAngles = new Vector3(-rotationY, transform.localEulerAngles.y, 0);
         }
     }
     
     
     void Start (){
         // Make the rigid body not change rotation
         if (rigidbody)
             rigidbody.freezeRotation = true;
     }
 }

I believe I have the right codes here, but when I test it, scrolling mouse wheel just does not enable me to zoom in or out.

Kindly help me by providing an advice and thank you in advice.

Thank you again!