make a new image folder inside the other the image folder...so the path will look like this: images/new_images
now, upload all the images to it, includeing the folders (like "icons", "polls", and "smilies")...now you got that part done, upload (and over right) the icons and the smilies that you want to use in the correct folder...now go into your Admin CP and go to:
Styles>Modify
choose the style you want to modify by clicking on [fonts/colors/etc]
scroll down tell you see "Image Paths" (or click the Jump Link that says "[image paths]") and just change the path to the new image folder...the smilies well also be fixed to the new ones, along with the other new images.
hope that helps