How to use a different list on button press?

I'm currently making a little Quiz about spelling.
The program shows a Question and 4 possible answers.
Now what I'm stuck on is that I don't know how to change the list that's being used.
I have 2 Lists of Questions: StamQuestions and StateQuestions.

 public void GiveAnswerA(object sender, EventArgs e)
 {
     if (TextAnswerA.Text == StamQuestions[numberQuestion].CorrectAnswer)
     {
         SetUI();
         score++;
     }
 }

 private void GiveAnswerB(object sender, EventArgs e)
 {
     if (TextAnswerB.Text == StamQuestions[numberQuestion].CorrectAnswer)
     {
         SetUI();
         score++;
     }
 }

 private void GiveAnswerC(object sender, EventArgs e)
 {
     if (TextAnswerC.Text == StamQuestions[numberQuestion].CorrectAnswer)
     {
         SetUI();
         score++;
     }
 }

 private void GiveAnswerD(object sender, EventArgs e)
 {
     if (TextAnswerD.Text == StamQuestions[numberQuestion].CorrectAnswer)
     {
         SetUI();
         score++;
     }
 }

 private void SetUI()
 {
     numberQuestion = rnd.Next(0, StamQuestions.Count);

     CurrentQuestion.Text = StamQuestions[numberQuestion].QuestionText;
     TextAnswerA.Text = StamQuestions[numberQuestion].Answers[0];
     TextAnswerB.Text = StamQuestions[numberQuestion].Answers[1];
     TextAnswerC.Text = StamQuestions[numberQuestion].Answers[2];
     TextAnswerD.Text = StamQuestions[numberQuestion].Answers[3];

     ResultAnswer.Text = "Punten : "+score.ToString();
 }

Now what I want to happen is that when I press a button, the StamQuestions get replaced by StateQuestions.

Any help would be appreciated!

Edit : Here is definition of the lists

        List<Question> StamQuestions = new List<Question>();
        List<Question> StateQuestion = new List<Question>();

In general you would just store a reference to the currently used list of questions, and swap that reference as needed.

Add another class-level variable for currentQuestions:

private List<Question> stamQuestions = new List<Question>(); 
private List<Question> stateQuestions = new List<Question>();
private List<Question> currentQuestions = stamQuestions;

Use currentQuestions everywhere, for example:

public void GiveAnswerA(object sender, EventArgs e)
{
    if (TextAnswerA.Text == currentQuestions[numberQuestion].CorrectAnswer)
    {
        SetUI();
        score++;
    }
}

Then swap to the other set as needed, I suspect in SetUI:

private void SetUI()
{
    currentQuestions = stateQuestions;

    numberQuestion = rnd.Next(0, currentQuestions.Count);
    CurrentQuestion.Text = currentQuestions[numberQuestion].QuestionText;
    TextAnswerA.Text = currentQuestions[numberQuestion].Answers[0];
    TextAnswerB.Text = currentQuestions[numberQuestion].Answers[1];
    TextAnswerC.Text = currentQuestions[numberQuestion].Answers[2];
    TextAnswerD.Text = currentQuestions[numberQuestion].Answers[3];
    ResultAnswer.Text = "Punten : "+score.ToString();
}

Or maybe you intended to flip/flop between lists in which case you could also do:

currentQuestions = (currentQuestions == stamQuestions) ? stateQuestions : stamQuestions;

Create a new private property:

private List<Question> Questions { get; set; }

then always use this property:

TextAnswerD.Text == Questions[numberQuestion].CorrectAnswer; 
...

And change it like this:

Questions = StamQuestions;

or

Questions = StateQuestion;