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How do I delete songs from an iPod nano?

I've tried opening the folder after I've connected the USB cable, and some songs which I do not have at all came up. And it was in my iPod's folder. And how do add the songs which I want? I tried downlaoding Number 1 by Tinchy Stryder ft. N-Dubz from beemp3, and it got onto the laptop. The I copied and pasted it from the main downloads folder to the iPod's folder and it worked but when I disconnected the USB, the song wasn't there. I double checked.

start > computer > removible device > browse your nano for music files right click and delete them or download itunes

Tinchy Stryder Ft N Dubz Number 1 (Fast Version)