How to change 2d texture when I press a button

 public Vector2 jumpforce = new Vector2(0,300);
 
 public Texture tex1;
 
 bool fixedAngle;
     
     void FixedUpdate () {
     
 if (Input.GetKeyDown (KeyCode.UpArrow)) {
 
             rigidbody2D.velocity=Vector2.zero;
             rigidbody2D.AddForce(jumpforce*1000);
             }
     if(Input.GetKeyDown(KeyCode.DownArrow)){
             renderer.material.mainTexture=tex1;
         }
 }

When I try this code, Player character not changing to the defined texture for DownArrow. Please Help me!