You can manage or cancel your subscriptions from the Amazon Underground app or Amazon Website or store.

Launch the Amazon Underground app, then open the menu item :

Select the Amazon Appstore menu item

Then choose Manage Subscriptions

This will show you a list of your current subscriptions. Tap the one you wish to remove, and select 'cancel', then confirm your choice,

You can also manage via the Amazon Website, or directly from your Fire tablet if you have one.

Method Process
Amazon website
  1. Go to Your Account, and select Apps and more under the Digital content and Devices section.
  2. From the menu on the left, select Your Subscriptions
Fire tablets
  1. Tap Apps, and then tap Store.
  2. Open the menu, and then tap Manage Subscriptions.
Amazon Underground app for Android
  1. Open the menu, expand the Amazon Appstore submenu, and then tap Manage Subscriptions.

Note: If you turn off auto-renewal for a subscription, you'll continue to have access until your current subscription period expires.