Hi  nauna,
Please refer below sample.
HTML
<div>   
    <asp:Image ID="Image1" ImageUrl="~/Files/Desert.jpg" runat="server" Height="100px"
        Width="100px" />
    <br />
    <asp:Button ID="btnSubmit" runat="server" Text="Rotate" OnClick="Rotate" />
</div>
Namespaces
C#
using System.IO;
using System.Drawing;
VB.Net
Imports System.Drawing
Code
C#
protected void Rotate(object sender, EventArgs e)
{
    string extension = Path.GetExtension(Image1.ImageUrl);
    string filename = Path.GetFileNameWithoutExtension(Image1.ImageUrl);
    string path = Server.MapPath(Image1.ImageUrl);
    string newpath = Server.MapPath(filename + "01" + extension);
    System.Drawing.Image img = System.Drawing.Image.FromFile(path);
    img.Save(newpath);
    img.RotateFlip(RotateFlipType.Rotate90FlipNone);
    img.Save(path);
    img.Dispose();
    Response.Redirect(Request.Url.AbsolutePath);
}
VB.Net
Protected Sub Rotate(ByVal sender As Object, ByVal e As EventArgs)
    Dim extension As String = System.IO.Path.GetExtension(Image1.ImageUrl)
    Dim filename As String = System.IO.Path.GetFileNameWithoutExtension(Image1.ImageUrl)
    Dim path As String = Server.MapPath(Image1.ImageUrl)
    Dim newpath As String = Server.MapPath(filename & "01" & extension)
    Dim img As System.Drawing.Image = System.Drawing.Image.FromFile(path)
    img.Save(newpath)
    img.RotateFlip(RotateFlipType.Rotate90FlipNone)
    img.Save(path)
    img.Dispose()
    Response.Redirect(Request.Url.AbsolutePath)
End Sub
Screenshot
