You can modify the subscription period (monthly, yearly, or forever) in the subscription settings of your device.
Even if you currently have an active subscription for a specific period, you can adjust its timing. Payments made for the previous subscription period will not be lost. As soon as the current subscription expires, the new paid period will automatically commence (or manually, in the case of Android).
SAU App for Apple
If the subscription was made through the SAU App on an iPhone, iPad, or MacBook, you can adjust the period on your device or in iTunes. A complete, up-to-date guide is available on the Apple Support portal
SAU App for Android
If the subscription was processed via the SAU App on an Android phone or tablet, transitioning to a new cycle automatically isn't possible. The easiest way is to cancel the current subscription, wait for its paid period to end (SAU will send you a notification email), and then re-subscribe. A comprehensive, current guide is available on the Google Store Support portal
SAU App for Huawei
Subscriptions via AppGallery are currently unsupported.
If the subscription was made on the SAU.app web portal, information about changing the subscription period can be found in the user profile