Detect edge collision...?

Hi everybody! I created a sprite that should walk across the screen with a costant speed, bouncing on edges with non-regular bounce (when touches an edge, it change direction to a random number)...

I wrote this so far:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PredaControllerScript : MonoBehaviour
 {
     float movX, movY;
     // Use this for initialization
     void Start()
     {
 
     }
 
     void FixedUpdate()
     {
 
 
         if (/*Sprite is Touching an Edge*/){
             changeDirection();
         }
 
         GetComponent<Rigidbody2D>().velocity = new Vector2(movX, movY);
     }
 
     void changeDirection()
     {
         int rand;
         movX = Random.Range(5, 15);
         movY = Random.Range(5, 15);
         do
         {
             rand = Random.Range(-10, +10);
             if (rand > 0)
                 movX = -movX;
         } while (rand == 0);
 
         do
         {
             rand = Random.Range(-10, +10);
             if (rand > 0)
                 movY = -movY;
         } while (rand == 0);
     }
 
 }

What should I write instead of /Sprite is Touching an Edge/ ?

I tried to use Edge Collider 2D, but I didn't understand how to use it... Thank you in advance! bye!

Ale