What exactly do you mean by that? If -instead of one particular image- you want to show some other image on a web page, then you need to change the HTML of that page to point to the other image. Creating the page dynamically using JSP (or some such technology) makes this easier.
Alternatively, you can replace the image file on the web server with the new image. [ December 18, 2008: Message edited by: Ulf Dittmer ]