You can downgrade your premium subscription back to the free version within your profile on this page https://www.fieldlevel.com/app/account/cancel
After canceling, you will continue to have access to your FieldLevel premium features until the end of your current billing cycle. Once the billing cycle has ended you will no longer have access to your premium features. Once cancelled you will still have access to all the free features of FieldLevel.
If you'd like to downgrade your subscription to a lower paying plan, you can do that from the plans page.
You can also find a link to the 'Cancel' or 'Change Plan' page under the 'Settings' area in your account.