Access parts of different scripts?

I need to access a script within another script, but I can't figure out how. I have a simple script that displays the current round, like so

 using UnityEngine;
 using System.Collections;
 
 public class GUITextHandler : MonoBehaviour
 {
    public GameObject gui;
     static int score;
 
     void update()
     {
 
         gui.GetComponent ("GUIText").text = "Score: " + score;
 
     }
 }

this is supposed to change the GUIText component to whatever I set it to.

then I have another script that launches a function called "WaveEnded" whenever the wave ends.

what do I put in the "WaveEnded" function to make it so whenever the wave ends, the "score" goes up by 1?

Thanks very much for your time