Cancelling is done from the administration area of the item the subscription belongs to, in four steps.

1. Click your username in the menu, then Administration.
2. Click Administration next to the item carrying the subscription: your CV for a player subscription, your team or your multigaming otherwise.
3. At the bottom of the page, in the Premium history block, click Update subscription.
4. You'll be redirected to the provider handling the payment. Click Cancel plan.

Your subscription stays active until the end of the period you already paid for.