how can i update my ipod touch 3rd generation to ios 5 ?

Welcome to the Apple Support Communities

Connect your iPod to the computer and iTunes will ask you to update the device

Connect iPod to iTunes using your computer. Click on iPod. Look for “update” you should be able to click that, and it will update to the next OS

Which model iPod touch do you have? If you aren't sure, this Apple doc can help ya -> Identifying iPod models

If you have the iPod touch (2nd generation), you won't be able to update to iOS 5, see this -> iPod touch: Which iOS 5 software features does my iPod touch support?

If you have a iPod touch (3rd generation) or later, see this Apple doc -> iOS: How to update your iPhone, iPad, or iPod touch

It is 3^rd generation, stated in post

I suspect you really have a 2G iPod. Those can ony go to 4.2.1.

Identifying iPod models

iPod touch (3rd generation)

iPod touch (3rd generation) features a 3.5-inch (diagonal) widescreen multi-touch display and 32 GB or 64 GB flash drive. You can browse the web with Safari and watch YouTube videos with Wi-Fi. You can also search, preview, and buy songs from the iTunes Wi-Fi Music Store on iPod touch.

The iPod touch (3rd generation) can be distinguished from iPod touch (2nd generation) by looking at the back of the device. In the text below the engraving, look for the model number. iPod touch (2nd generation) is model A1288, and iPod touch (3rd generation) is model A1318.

ryanrocks9654 wrote:

It is 3^rd generation, stated in post

Hhhmmm!

We've seen countless (and I mean countless) posts here claiming that someone has a 3rd gen Touch, only to find out that it's actually a 2nd gen Touch. Just because the post says it is, doesn't mean it really is.

In fact, as lllaass says (below now), it's more likely to be a 2nd gen Touch.

Let's see if Karen comes back with any more information.

I'd wager a cold adult beverage is an 8 gig 2nd gen...

I would not bet on that. It could a a 16 or 32 GB 2G.