That comes with iOS 5 and later.
To update if it can be updated:
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
That means you do not have iOS 5 or later installed.
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