Hi,
i've figured out what to do as no-one would help me either, but you really do need a computer.
You need to sync your ipod to any laptop or computer, then once it's all loaded, click the 'store' button at the top of the screen. Then click on 'View my account (Your email is here).
You do this, and then type in your itunes password.
This takes you to a screen which says with lots of options to review your account. The one you want is 'purchase history'.
It will tell you what you've purchased etc, and how much they cost. In red it says something about you owe a balance or something, anyway, there should be a box saying that you agree to it or something, and you might need to go to the option on the screen after you've put in your password that says edit payment information.
I'm really sorry, but i've forgotten the excact details.
So it's either purchase history, or edit payment information. You just click done at the bottom of the screen adn it's sorted!