Which iPod do you have? You posted in the iPod classic forum, but your product listing shows you have an iPod touch.
If you have the iPod touch, go to Settings > General > Reset > Erase All Content and Settings.
If you have the iPod classic (though you can also use this method for the iPod touch), connect to to the computer and launch iTunes. It should appear in the sidebar on the left. Then click the iPod's menu in the sidebar, and click Restore.
If you don't see the sidebar, follow: iTunes 11: Show Sidebar and Status Bar