If losing the data in the apps is not a concern, delete them from the iPod and redownload them via the App Store. Or download them on your computer through iTunes and sync them to the iPod. You may also want to consider going into Settings->Store, and verifying that you are signed into the correct account. Perhaps someone else used your iPod touch without your knowledge and you have been unwittingly downloading stuff under their account? If you try to update apps that were not purchased under one account and are not signed in to the account which they were initially bought under, you cannot update them.