How to aim bullets with arrow keys and move with wasd

I followed the TornadoTwins tutorial but I want my worm to aim up when I press the up arrow and vice versa, any help? If the aiming could be increments too that would be great.
function Update ()
{
var controller : CharacterController = GetComponent(CharacterController);

//Rotate around 7 - axis
transform.Rotate(0, Input.GetAxis ("Horizontal") * rotateSpeed, 0);

//Move forward / backward
var forward = transform.TransformDirection(Vector3.forward);
var curSpeed = speed* Input.GetAxis ("Vertical");
controller.SimpleMove(forward * curSpeed);

if(Input.GetButtonDown("Jump"))
{
	var bullet = Instantiate(bulletPrefab,transform.Find("spawnpoint").transform.position, Quaternion.identity);
	bullet.tag = "wormProjectile";
	bullet.rigidbody.AddForce(transform.forward * 1850);
	explosion1.Play();
}

//{
//	rotate += 2;
//	bullet.rigidbody.transform.rotate(Vector3.up * Time.deltaTime, Space.World);
//}

}

There is my script.

Define yourself a new axis in the input manager. Use the ‘vertical’ axis as template for your new axis.

Then in your code you can use that axis in the same way as you would use the ‘vertical’ axis - but both will be independent of each other.