How to stop subscription of Pandora/an app on apple store

http://support.apple.com/kb/HT4098

To manage auto-renewing subscriptions:

1. From your device's Home screen, tap App Store.
2. Tap Featured at the bottom of the screen.
3. Scroll to the bottom of the page.
4. Tap the Apple ID button in the lower-left corner. (If you are not signed in, tap the Sign In button, and sign in with your Apple ID. Then, scroll back to the bottom of the page, and tap the Apple ID button.)
5. Tap the View Apple ID button.
6. Enter your password and tap OK.
7. From the main account page, scroll down and tap Manage App Subscriptions. If you don't have app subscriptions this button will not be displayed.
8. From the Manage App Subscription page on your iPhone, iPad, or iPod, tap the app that you would like to manage.
9. Depending on the app, you'll have the option to manage different subscription categories.
   
   
    
10. Once you tap a subscription category, you will see the current subscription status and available options.
    
    


11. Tap the desired renewal option to select it, and then tap Subscribe.
    
    
     
12. You will see a confirmation window asking you to confirm your purchase.
13. Tap Confirm to proceed with your purchase.