I assume that "you" can't find them. It is a hidden folder, meaning the OS can see it but the user can't. The only way I know how to access it is through the terminal. I moved my incoming directory to avoid this problem. Just copy the files via the terminal to another directory and then delete that "incoming" directory, and you should be good to go. Of course, make sure aMule is linked to that new directory. The terminal is located in Applications -> Utilities -> Terminal.