it wont let me update ios

when ever i try to get apps from the app store, it says " This application requires iOS 5.0 or later. You must update to iOS 5.0 in order to download and use this application." iv'e asked all my friends and they had no trouble updating it on their ipod. its brand new. shall i bring my ipod to an apple store or can you tell me how to do it?

i go to settings, then my friends told me to go to software updates but i dont have that.

thank you if you can help me with this!

~bethan