Open Explorer.exe file in Resource Hacker.
Search for the bitmap which u want to change, save it on HDD, open it in MSpaint or other image editing s/w, edit the image as u want, save it, then replace the bitmap with ur new one using resource hacker, save the explorer.exe file on some other drive, cauz windows will warn u that this file is being used by someother process, open command prompt then open task manager, stop the explorer.exe process, now u can safely replace original explorer.exe with the new edited explorer.exe file, now log off and u can see the new image...