How do you access Sprite renderer flip in a script?

I've been trying to access this through a script. Easy way?

 using UnityEngine;
 using System.Collections;
 
 public class SepiksStare : MonoBehaviour {
 
     public Transform playerTransform;
     public int RotationLock = 90;
     SpriteRenderer sr;
 
 
 
 
     void Start () {
         sr = gameObject.GetComponent<SpriteRenderer> ();
     }
     void Flip () {
 
 
     }
 
     // Update is called once per frame
     void Update () {
         //Debug.Log (transform.rotation.z);
         Vector3 difference = playerTransform.position - transform.position;
         difference.Normalize ();
 
         float rotZ = Mathf.Atan2 (difference.y, difference.x) * Mathf.Rad2Deg;
         transform.rotation = Quaternion.Euler (0f, 0f, rotZ + RotationLock);
         //Debug.Log (transform.localEulerAngles.z);



         if (transform.localEulerAngles.z >= 90) { 
             sr.flipY (); //THIS RIGHT HERE ERRORS Saying SpriteRenderer does not contain a definition for 'flipY'
         }
 
 
     }
 }

SpriteRenderer does not contain a definition for 'flipY'