How can I change my credit card data? My credit card was stolen and I want to use a new one for paying apps. I don't know how to do that.
One way is to go to http://apple.com, click "Store" in the top menu and then click "Account" and "View Account" as in the below screenshot.
Under "Account settings" there is the choice to "Change your default shipping or billing info", click that link and then enter your Apple ID e-mail and password to login. You'll see a box with the heading "Payment Information" under Account Information, click the Edit button there.
You will then see a form for entering your payment information, add your new card details on the right and click save. The card you enter here will be used on the Apple Online Store, iTunes and Apple App Store.
Just open iTunes
Goto the store and click on your account/email.
Click Account menu item and log in. Now you can change your payment details.