Help needed in picture box.

hello.

when i load picture in picture box its fine, but when i load another picture the previous one remains there, and it seems

that images overlapping each other after the second image and so on.....

i have googled and also used ,

if (picbox1.Image != null)
            {
                picbox1.Refresh();
                picbox1.Image.Dispose();
                picbox1.Image = null;
                this.Invalidate();
                this.Update();
               
            }

but it is still not working .

please solve the problem.

thx in advance