How to change the Width and Height in the script C#? (New Gui Unity 4.6 beta)

Hello, how to change the Width and Height in new gui:

32474-width_height.jpg

I tried:

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class RectTest : MonoBehaviour {
	public Button MyButton;

	void Start () {
		MyButton.height = 700;									//not working
		MyButton.transform.height = 700;						//not working
		MyButton.transform.position.height = 700;				//not working
		MyButton.gameObject.transform.position.height = 700;	//not working
	}
}

Thanks!

RectTransform t = transform as RectTransform;
Vector2 dimension = t.sizeDelta;
dimension.x = preferredWidth;
dimension.y = preferredHeight;
t.sizeDelta = dimension;

There is no way to change that ://