Quiz Game: How to replace Text with Images?

So, I followed an official Unity tutorial about making a Quiz Game. I successfully followed each and every step and it works great. Now I want to replace the text on the buttons with images. I tried dragging one of the images into the button UI but it ends up changing all of it instead of just one single button. So how do I replace the text with an image on a button?

TUTORIAL LINK: http://www.unity3d.com/learn/tutorials/topics/scripting/quiz-game-intro-and-setup

@bryanllanes its because there is probably one or few button elements used to create all the choices, so buttons text is being changed at the runtime through code. look in the code where he sets the text of the buttons. when you find. instead of text start replacing with the images you want to set.
if you need help with changing the image through code let me know.

When I change it to factText.sprite, currentQuestion.vraag gives an error that says “Cannot implicitly convert type ‘UnityEngine.UI- 1Image’ to ‘UnityEngine.sprite’.”

[System.Serializable]
public class Questions {
 public string fact;
 public string answerOne;
 public string answerTwo;
 public string answerThree;
 public string answerFour;
 public bool isOne;
 public bool isTwo;
 public bool isThree;
 public bool isFour;
}

This is the one that’s used for the text one.

using UnityEngine.UI;
[System.Serializable]
public class ImageVragen
{
 public Image vraag;
 public Image antwoord1;
 public Image antwoord2;
 public Image antwoord3;
 public Image antwoord4;
 public bool isOne;
 public bool isTwo;
 public bool isThree;
 public bool isFour;
}

And this is the one that is used for the image one

(also thank you for trying to help me so far, much appreciated)