How change tile skin

Hi evryone! I'm wondering where in warcraft world editor I can find where to change the tiles skins. I just cant seem to find it anywhere
Can somone please post a picture of where or tell me where. It would be awsome if you could Thank you.

Tutorials are your friend so is google. Don't give up if you don't get it in one search. You may need to take an hour to find it.

I have been looking very long. I cant find anything

Took me under a minute.
The Helper Tutorials is the best for tutorials. Go figure.

Creating Custom Tile Sets

Figure out the path of the terrain tile texture you're wanting to change, import the new tile as a .blp file and change the path to that of the tile you wish to replace. If that made no sense, then follow Gilles' suggestion.