To update connect to your computer and update via iTunes oiif the model allows it.
A 1G iPod can go to iOS 3.1.3
A 2G to 4.2.1. Requires iTunes version 10.X. That requires a Mac with OSX 10.5.8 or later. With 1OSX 10.4.11 you can only go to iTunes 9.X which gets you as high as iOS 4.1
A 3G to 5.1.1 Requires iTunes version 10.5 or later
A 4G to 6 Requires iTunes version 10.7 or later. That requires a Mac with OSX 10.6.8 or later
Vital Resources For Your iDevice (Updating, Apple ID, and iCloud)
A. Upgrading iOS
4. iPad Support
a. Updating Your iOS to Version 6.0.x from iOS 5
Tap Settings > General > Software Update
If an update is available there will be an active Update button. If you are current,
then you will see a gray screen with a message saying your are up to date.
b. If you are still using iOS 4 — Updating your device to iOS 5 or later.
c. Resolving update problems
1. Apple ID FAQ
E. User Manuals
3. iPod Touches