How can I erase the music on prev. owner's ipod so I can put my music on

I bought an Ipod Shuffle 4th Gen 2mb on ebay, and the seller's music was still on it.

I want to erase his music and put my Itunes on it. I know it is possible, cos I did it on another ipod.

Don't know where to find button to click to delete it.

Have called Apple, have asked support, no one answers me.

Thanks!