If you want to renew the Subscription before expiration date (when it would Auto Renew automatically) you can Renew your subscription Manually at any time you want.
You can do that only if subscription is Active.
To Renew your Subscription, go to the Subscriptions page (link) and select the subscription you want to Manage. You will see the below screen. Simply click the Renew Now button and a new order will be created for that subscription for the next period.