How to implement a flip direction to my 2D character controller?

I am new to C# programming and I have my character controller script here, but how can I make the sprite flip direction when controlling it? This is what I have so far.

public class CharacterController : MonoBehaviour {

 public float speed = 1.0f;
 public string axisHorizontal = "Horizontal";
 public string axisVertical = "Vertical";
 public Animator anim;

 // Use this for initialization
 void Start () {
     anim = gameObject.GetComponent<Animator> ();
 
 }
 
 // Update is called once per frame
 void Update () {

     anim.SetFloat("Speed", Mathf.Abs(Input.GetAxis(axisHorizontal)));
     anim.SetFloat("Speed", Mathf.Abs(Input.GetAxis(axisVertical)));

     
     transform.position += transform.right *Input.GetAxis(axisHorizontal)* speed * Time.deltaTime;
     transform.position += transform.up *Input.GetAxis(axisVertical)* speed * Time.deltaTime;

 }

}