No Cancellation required for Trial Accounts
Trial Accounts do not have any subscription - the account will simply run out at the end of the trial, as indicated by the top red banner inside the software.
Where can I cancel? Cancellation in Account Management
The account can be canceled at any time within the account management via the top right figure:
There you can click on "terminate" beneath your current plan:
In order to cut the integration with Amazon's API, you can revoke the rights in Seller Central as shown here.
When will the account run out after canceling?
After you terminate the account, it will continue to run until the end of your individual monthly cycle.
If you upgraded to your plan on December 26 and cancel on December 29 (or any other day within your cycle), the account will only run out on January 25.
Example view after cancelation:
You can reactivate a canceled account at any time at the same location. All the previously assembled data will still be available after the reactivation.