Vertical Background Scroll

Hi,
I am currently using this code below to scroll my background from left to right.
Can anybody tell me if it is possible to modify this script to make the background scroll from top to bottom?
I got this script from a tutorial, and i have tried searching for other answers but they all seem to make it alot more complicated than this.

Many Thanks

using UnityEngine;
using System.Collections;

public class ScrollScript : MonoBehaviour 
{
	public float speed = 0;

	void Update ()

	{
			renderer.material.mainTextureOffset = new Vector2(Time.time * speed, 0f);
	}
}

using UnityEngine;
using System.Collections;

public class ScrollScript : MonoBehaviour 
{
    public float speed = 0;
 
    void Update ()
 
    {
         renderer.material.mainTextureOffset = new Vector2(0f, -Time.time * speed);
    }
}