When you subscribe to a plan, you can cancel your subscription at any time.
The option is available here (Manager website > My Account > My subscriptions).
Once the subscription is cancelled, your account will stay active for the already paid period.
For instance, if you take a monthly subscription and only need it for one month, after subscribing you can click on "Cancel this subscription". This way, you can make sure the subscription will only run for the paid month and you won't be billed afterward.
To learn how to create a subscription, check here.
You can find all informations regarding subscriptions here.