The image is coming from my picture box but the iamges is bigger than my screen, this is my code how can i get it to fit the screen best?

Code:
 Dim fileName As String = "WallPaper"
        Dim imagePath As String = IO.Path.Combine(Environment.ExpandEnvironmentVariables("%windir%\Web\Wallpaper"), fileName)
        PictureBox1.Image.Save(imagePath, System.Drawing.Imaging.ImageFormat.Bmp)
        SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, imagePath, SPIF_UPDATEINIFILE)