Is it possible to upgrade my apple products?

By upgrade i am NOT talking about over clocking or hardware upgrades, but what I want to ask is if it is possible to trade in my (older not old but still available on Apple's website) hand those in, and get a better version of that product. More specifically, I am thinking about upgrading my iPod touch 5G 16 GB to the iPod touch 5 to 32 GB, with the rear camera. I am only asking this because my friend recently upgraded his 3G to the 3GS, because it had a cracked screen, and they charged €150. At the time, the 3G cost around €300, or something like that, but my main question is, is it possible?