Simple error but I'm just a begginer and cant figure this out, due to outdated API.

Hello helper, and thanks for helping me, so my problem is my playing sound effects for fire sound, are too low for enemies and players, when i run the game and i try to shoot using my left click mouse the fire sound is really low and i'm trying to control its volume by a script, same for the enemies fire sound so here is my code below, and error message i get.

Error Message : error CS0120: An object reference is required to access non-static member `UnityEngine.AudioSource.volume'

using UnityEngine; using System.Collections;

public class PlayerController : MonoBehaviour { //A variable(box in inspector where you can adjust the speed of the moving character(Player)) public float speed = 5.0f; public float padding = 1; public GameObject bulletShot; private float xmax = 78; private float xmin = -79; public float projectileSpeed = 10; public float projectileRepeatRate = 0.2f; public float health = 350; public AudioClip fireSound;

 void Start() {

 Camera camera = Camera.main;
 float distance = transform.position.z - camera.transform.position.z;
 xmin = camera.ViewportToWorldPoint(new Vector3(0,0,distance)).x + padding;
 xmax = camera.ViewportToWorldPoint(new Vector3(1,1,distance)).x + padding;
 }


 void Fire() {

 Vector3 offSet = new Vector3 (-2,0.40f,0);
 GameObject beam = (GameObject)Instantiate(bulletShot, transform.position + offSet, Quaternion.identity);
 beam.GetComponent<Rigidbody2D>().velocity = new Vector3 (-projectileSpeed,0,0);
 fireSound = AudioSource.volume(2,3);
 AudioSource.PlayClipAtPoint(fireSound, transform.position);
 }




 // Update is called once per frame
 void Update () {
 if (Input.GetMouseButtonDown(0)) {

 InvokeRepeating("Fire", 0.0001f, projectileRepeatRate);

 }
 if (Input.GetMouseButtonUp(0)) {

 CancelInvoke("Fire");

 }
 //Allowing the player to move in the X-axis
 if (Input.GetKey(KeyCode.A) || Input.GetKey(KeyCode.LeftArrow)) {
 transform.position = new Vector3 (
 Mathf.Clamp(transform.position.x - speed * Time.deltaTime, xmin,xmax),
 transform.position.y,
 transform.position.z
 );

 } 
  if (Input.GetKey(KeyCode.D) || Input.GetKey(KeyCode.RightArrow)) {
 // Rotate the object around its local X axis at 1 degree per second
 transform.position = new Vector3 (

 Mathf.Clamp(transform.position.x + speed* Time.deltaTime, xmin, xmax),
 transform.position.y,
 transform.position.z
 );

 }


 }

 void OnTriggerEnter2D (Collider2D collider){

 Projectile missile = collider.gameObject.GetComponent<Projectile>();

 if (missile) {
 health -= missile.GetDamage();
 missile.Hit();
 if (health <= 0 ) {


 Destroy(gameObject);
 }

 }
 }
 }