To subscribe Fire Premium, tap the profile icon on the right bottom of the screen and tap Become Premium icon on the profile screen. Select one of packages, enter your Apple ID or Google Play Store ID and complete your payment. You can immediately start to use Fire Premium functions.
NOTE: Deleting the Fire app does not delete your account. If you subscribe Fire Premium using your Apple ID or Google Play Store ID, deleting the app and/or your account does not cancel your subscription. You need to cancel your recurring subscription from iTunes or Google Play using your ID.