Q: how do I update my ipod 3rd generation ios 3.1.2

Update Server

Try:

- Powering off and then back on your router.

- iTunes for Windows: iTunes cannot contact the iPhone, iPad, or iPod software update server

- Change the DNS to either Google's or Open DNS servers

Public DNS — Google Developers

OpenDNS IP Addresses

- For one user uninstalling/reinstalling iTunes resolved the problem

- Try on another computer/network

- Wait if it is an Apple problem

Note your iPod may already be maxed out for iOS

To update

The Settings>General>Software Update comes with iOS 5 and later.

Connect the iPod to your computer and update via iTunes as far as your iPod model allows

iOS: How to update your iPhone, iPad, or iPod touch

A 1G iPod can go to iOS 2.2 via iTunes and iOS 3.1.3 via

Purchasing iOS 3.1 Software Update for iPod touch (1st generation)       

https://buy.itunes.apple.com/WebObjects/MZFinance.woa/wa/touchLegacyLandingPage

- A 2G to 4.2.1. Requires iTunes version 1o or higher. If a Mac it requires OSX 10.5.8 or later.

- A 3G to 5.1.1  Requires iTunes version 10.5 or later

Identifying iPod models