To cancel or unsubscribe from an app, go click on the Apps icon on the Home screen:
Click on the Account tab in the bottom right hand corner.
From here you can manage credit cards on file to use for subscriptions, see the list of apps you are subscribed to, as well as invoices created and their status.
Next to each app, you'll see Unsubscribe option.
Tap on the unsubscribe and follow the prompts on the next screen.
You should see a note about your subscription being cancelled and will ask you to uninstall the app. Once you click on Uninstall, the app will be removed from your device.