To delete your account, click on the Menu button in the upper-right corner of the browser and then click Settings.
In the Settings menu, click the Billing tab and then click the top Edit button to the right of Subscription Active.
In the new dialogue box that appears, click Yes under the question, Do you want to pause your subscription?
This will cause your subscription to be paused, which will prevent Targetable from creating new content for you, and pause all payments to your account.