Connect your ipod to your computer and go to Start>My computer. You should see your ipod listed as one of the drives. Double click on it and a folder should open with all the files listed in it. You should be able to delete them from there.

Or, you should be able to delete them from the ipod itself. Just turn it on and there should be an option in the menu to delete the files.

Then there may also be a reset button on it that you can press(possibly a tiny hole that you can stick a pin in) that'll reset it and erase all the files.

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