In order to terminate your paid account, you need to email email@example.com or your dedicated manager and request the cancellation.
If you want to downgrade your paid account to the free one, you can follow this guide to do so. Some features will no longer be available in the Free plan comparing to the paid ones. Make sure you do not have more than 2 users or the amount of records do not go over 2500. Otherwise, your account will be locked due to plan limitations.