Textures are found in textures.pck in your element folder. To extract the .pck file, use sPCK.exe which you can find
[Only registered and activated users can see links. Click Here To Register...].
I've given a short description before about how to use sPCK in another guide I made
[Only registered and activated users can see links. Click Here To Register...]. The usage is the same.
There are various tutorials around regarding modifying textures for PWI, just search Google.
Cheers