Okay...so you're talking about your "Apple ID," which is different from the name of your iPod.
In iTunes while you're viewing the Store, there should be a button near the top right that says "Sign In" or contains your Apple ID, which is an e-mail address. This is what you want to change, right?
Click on the button with your Apple ID in it (or sign in first if you're not already) and enter your password, then click "View Account." It'll take you to a screen where you can enter a new e-mail address which will also be your new Apple ID.
Is that what you're looking for?