When a customer signs up for a subscription a subscription is created in the backend of your website. So both an order is created and a subscription. Managing subscriptions is very similar to how orders are managed. Please follow the below steps:
From your main menu go to Shop/eCommerce and then Subscriptions.
You will land on the all subscriptions page which has a listing of all your subscriptions. You can take quick actions like cancelling a subscription by simply selecting the checkbox next to the subscription and then in the dropdown at the top and bottom of the table selecting your action, and then clicking the Apply button next to the dropdown. Or you can hover over a subscription and you can quickly cancel or suspend the subscription.
By clicking on the subscription number it will take you to the subscription detail page. On the Subscription detail page you can edit a whole range of information for a given subscription. This includes the customers details, the products they purchased, the billing period and the next payment date.
Once you are happy with the changes click the Update button.