Changing Update C#

Unity Engine
1

Does any one know how to change Update to something else for example:
I have this code which lets my object move… and i would like to change that code from (to make it stop)
THIS
transform.position += Vector3.up * Time.deltaTimespeed;
TO THIS
transform.position -= Vector3.up * Time.deltaTimespeed;
On Collision. This is my code:

    float speed = 5.0f;
   

    void Update() {
       
        transform.position += Vector3.up * Time.deltaTime*speed;
    }
    void OnCollisionEnter2D(Collision2D collision) {
        DestroyObject(collision.gameObject);
        transform.position -= Vector3.up * Time.deltaTime*speed;


    }

    public void SetSpeed(float modifier)
    {
        speed = 5.0f + modifier;
    }

}
2

I would create a variable, like direction, which is either 1 or -1, in CollisionEnter2D I would set it to -1, then I’d multiply the whole Vector3.up * Time.deltaTime * speed thing with it

3

not sure if this is what you’re after. but it might get you on the right path

float speed = 5.0f;
bool isFwd = true;
  
    void Update() {
       if(isFwd)
       {
        transform.position += Vector3.up * Time.deltaTime*speed;
        }else
        {
        transform.position -= Vector3.up * Time.deltaTime*speed;
        }
    }
   
    void OnCollisionEnter2D(Collision2D collision) {
        DestroyObject(collision.gameObject);
        isFwd = false;
    }
    public void SetSpeed(float modifier)
    {
        speed = 5.0f + modifier;
    }
}