You can call the RotateFlip method of the Image object in order to rotate your images 90, 180 and 270 degrees in your applications. The RotateFlip method takes RotateFlipType enum as parameter. In these enums, you can call the ones with 'Flip' if you want to rotate them on X or Y axises:
 private void Form1_Load(object sender, EventArgs e)
        {
            Image img = Image.FromFile(@"C:\a.jpg");
            img.RotateFlip(RotateFlipType.Rotate90FlipX);
            pictureBox1.Image = img;
        }