On licento.com, open Premium in your account and choose «Manage your subscription»: you cancel there and keep Premium to the end of what you paid for.
«Manage your subscription» opens the page of Stripe, our payment provider, where you can cancel, stop renewing, switch between monthly and yearly, or change your card.
A subscription renews on its own until you cancel. After you cancel, Premium runs to the end of the period you paid for and then stops. The exams you own are not affected: their book and your scores stay yours.
The Premium that comes with buying an exam is not a subscription. It ends by itself, and there is nothing to cancel.