Changing the sprite PNG file

I tried to enhance my featured listing with editing the sprite png file, which I done, but I cannot replace the file as it comes back with file already exists. Any ideas? I notice that the png file has featured already on the top of the file, but this doesnt show in the drop down enhancments list in the listing admin area. Or is there a way of changing the file completly with a ribbon, which I see on a lot of other sites?

I am concerned that the featured listing doesnt really stand out well enough for it to be called a featured listng except being listed in the featured areas. I have already changed the background colours to help with the enhancements (thank you who wever poted that), which show on the front page. Having searched around the forum quite a bit, does anyone have any other suggestions for making the featured listing stand out more?

Many thanks Paul