How do I change the fount size of GUI

I looked around on the net and I haven’t found much that works with a string in the GUI text this is one of the things I have tried.

public string names = "Press F to toggle the sink";

void OnGUI()	
	{
		if(on == true)
		{
			GUI.Label(new Rect((Screen.width / 2) - 0, (Screen.height / 2) + 0, 200, 200), names, guiText.fontSize = 50);
		}
	}

Try using GUIStyle.fontSize

public string names = "Press F to toggle the sink";

void OnGUI()
   {
      if (on == true) {
         GUIStyle myStyle = new GUIStyle();
         myStyle.fontSize = 10; //change to font size
         GUI.Label(new Rect((Screen.width / 2) - 0, (Screen.height / 2) + 0, 200, 200), names, myStyle);
   }
}