for (int i = 1; i < trainingImages.ToArray().Length + 1; i++)
{
    trainingImages.ToArray()[i - 1].Save(Application.StartupPath + "/TrainedFaces/eladena/face" + i + ".bmp");
    File.AppendAllText(Application.StartupPath + "/TrainedFaces/TrainedLabels.txt", labels.ToArray()[i - 1] + "%");
}
MessageBox.Show(textBox1.Text + "´s face detected and added :)", "Training OK", MessageBoxButtons.OK, MessageBoxIcon.Information);

string[] filePaths = Directory.GetFiles(Application.StartupPath + "/TrainedFaces/", "*.bmp");
foreach (string filePath in filePaths)
{
    if (filePath.Contains(".bmp"))
        File.Delete(filePath);
}