Setting a speed for a Random Images

I'm trying to create matching game. This game consist of three picture boxes where each picture boxes shows random images that changes 3 times within a second. The objective of this game is to match all images in each picture box to beat the game.

This code is somewhat working. It is running but I cannot get the speed setting to work. It is currently just running 1 image per second. The ChangeImage() is turned off at the moment since I cannot get it to work. Please excuse my explanation.

To start off, I created a list of images where my pictures are added:

 private List<Bitmap> paths = new List<Bitmap>();


    public Form1()
    {
        InitializeComponent();
        paths.Add(Properties.Resources.Pumpkin);
        paths.Add(Properties.Resources.Cherry);
        paths.Add(Properties.Resources.Pineapple);
        paths.Add(Properties.Resources.Apples);
    }

I also have an event handler to produce the random image in a picture box:

private void timer2_Tick(object sender, EventArgs e)
        {
            picBox2.Image = paths[randomImg2.Next(0, paths.Count)];
        }

and to start the game, I have another even handler that allow the player to select the speed of the images' cycle:

   private void btnPlay_Click(object sender, EventArgs e)
        {
            timer1.Enabled = true;
            if (radThreeSpeed.Checked)
            {
                ChangeImage(3);
            }

            if (radFiveSpeed.Checked)
            {
                ChangeImage(5);
            }
        }

private void ChangeImage(int loop)
            {
                int imageCount = 1;
                while (imageCount <= loop)
                {
                    picBox1.Image = paths[randomImg1.Next(0, paths.Count)];
                    imageCount++;
                }
            }

My question is, how can I get this to work so that the image changes 3x or 5x or however I would like it to be within a second?