Follow these steps to cancel your subscription:

On iOS 12 or more recent:

  1. Open the App Store.
  2. Tap on the picture in the right-hand corner.
  3. Select "Manage Subscriptions".
  4. Choose Joy of Reading and tap "Cancel subscription".

On any previous iOs:

  1. Open the Settings icon on your device (the grey one).
  2. Scroll down to iTunes & App Store.
  3. Select our iTunes ID or login.
  4. Enter your password.
  5. Scroll down to "Subscriptions".
  6. Find Joy of Reading.
  7. Tap "Cancel subscription"

The official Apple step-by-step is available here.