I own an ipod touch version 3.1.3 can I update the ios?

To update

Connect the iPod to your computer and update via iTunes

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. If a Mac it requires 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

Are you sure you have a 2G?

Identifying iPod models

You have a 1G iPod. Those can only go to 3.1.3

A MB376LL is a 1G iPod, with 1G meaning first generation (original) iPod touch

There are not than many apps that now work with 3.1.3

It still works fine for music, video and other things.