Q: how do i download apps to my ipod touch when it says app requires ios 4.0

If it's an original iPod touch, you can't. Otherwise, update it to iOS 4.2.1, 5.1.1, or 6.0.1 from iTunes on a computer.

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Connect the iPod to your computer and update via iTunes if your model allows going to iOS 4

iTunes 10 for Windows: Update and restore software on iPod, iPhone, or iPad

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)

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

Identifying iPod models

I haven't personally confirmed this(I don't have an iOS device), but some people have reported being offered to update devices to iOS 6 from iTunes 10.6.3 running on 10.5.8, and it is definitely possible to sync them unless they list 10.6.8 as an original requirement.

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