Change properties of Web page controls in ASPX.CS

In ASPX.CS

System.Web.UI.HtmlControls.HtmlImage IMG  = (System.Web.UI.HtmlControls.HtmlImage)Page.FindControl("IMG1");
    IMG.Attributes.Add("src", "image/TopPic1.gif");

In ASPX

<img src="image/TopPic.gif" border="0" runat="server" width="630" height="79" usemap="#Navigation"
      >