To cancel any of your drivers' subscription, you should first delete the vehicle from the Dashboard.
After deleting the vehicle, go to the billing dashboard via Account > Billing.
In the billing dashboard, go to Services > My Services.
You will see a list of your drivers' subscriptions and you will be able to request cancellation of the licenses via the View Details button.
If your subscriptions have differing due dates, you will usually want to request cancellation for the ones with the earlier due dates (so that your remaining licenses are the ones that end later).
Once a cancellation request has been submitted, you will not be invoiced for the subscriptions. And if you need to add them back, simply place a new order with us.