The iPod's registration is synchronised to your computer when it is initially set up, and is removable by reformatting the device. By reformatting the iPod, all information is cleared from its hard drive and is restored to original settings. Unregistering your iPod is necessary when changing the default operating system as the system files differ between PCs and Macs; registering the iPod with either operating system renders it incompatible with the other. Once the iPod's registration is removed, the iPod Setup Assistant will appear when the device is connected to a computer, as iTunes will recognise the iPod as a new device.
Insert the docking cable into your iPod and the USB port on your Mac or PC. iTunes will open once the device is plugged in and detected.
Right-click the iPod tab in iTunes and click "Restore." Alternately, click the iPod tab in iTunes and click "Restore."
Click the "Restore" or "Restore and Update" icon on the pop-up dialogue box. According to Apple, selecting the first option restores the iPod to the original firmware, whereas the latter option restores the iPod and updates it to the latest firmware version.
Right-click the iPod tab and select "Eject" on the pop-up menu after the device restoration finishes. The iPod's screen will display the status of the restoration process.
Re-register the iPod at the Apple Registration site using a new Apple account (see Resources for link) to remove any previously registered information from your Apple account.