You can delete your account by the following:
iSharing menu (top left) > Settings > Delete my account
If you have signed up for the Premium Service, you need to cancel your subscription, so that you will not be charged after deleting your account. Subscription payments are managed by the Apple AppStore and the Google Play Store. Canceling your subscription can be done by the following:
Settings > iTunes & App Store > Apple ID > View Apple ID > SUBSCRIPTIONS > Manage
*Google Play Store
Play Store > menu(top left) >Subscriptions > iSharing > Cancel subscription
Please note that when you delete your account, your information will be removed completely and you will have to sign up again if you choose to give iSharing another try in the future.