Q: can't not downloand

I suspect you have the original iPod touch. Those can only go to iOS 2.2 via iTunes and 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 10 or higher. If a Mac it requires OSX 10.5.8 or later.

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

Identifying iPod models

The original iPod touch does not have an internal speaker and does not have volume buttons on upper left edge