How to input a current resolution on GuiText?

You can access your current resolution through

 Screen.width;
 Screen.height;

If you have a script that references a GUIText, you can change its text through

 myGUIText.text = "newText";

...putting these two together, you'll get something that looks like this;

 public GUIText m_text;
 void Update () 
 {
     m_text.text = "width: " + Screen.width + ", height: " + Screen.height;
 }

Hope this helps.