Plutonium

I been trying to change he menu background image of iw5, i already change the extension to dds to iwi, already located the files app and the /storage/iw5/image and created a loose folder with the image, but nothing happens and if i try to replace the original img with the new with the same name, at launching pluto it fetches the files and overwrites it, i already check the docs but i dont know if im missing something