If you are now in a different country (you have to be in a country to use its store) then you can log into your account via the Store > View Account option on your computer's iTunes : Change the country of your iTunes Store, App Store, iBooks Store, and Mac App Store account
If you have a balance on your account then you will first have to contact iTunes Support to get it removed : http://www.apple.com/support/itunes/contact/
You also won't be able to change countries if you iTunes Match or outstanding season passes or rentals.
Double-check that all the services that you have now will be available in the new country. Also make sure that you have a credit card in the new country. Your payment on file with Apple must match your Apple ID country. You don't have to change it. You can just create a new Apple ID in the new country. It gets to be a hassle after a while when you have apps in one country and apps in another. Everything still works, you just have to change countries in the store apps frequently.