You can easily change your subscription plan through your iPhone or iPad settings. To do so, please follow these steps:
Open the "Settings" on your device.
Tap your "Apple ID" at the top.
Select "Subscriptions". If you don’t see "Subscriptions", select "iTunes & App Store" → tap your "Apple ID" → choose "View Apple ID" and sign in → scroll down and tap "Subscriptions".
Find and tap "Walking" app subscription.
Tap "See All Plans".
Select the plan that best suits your needs.
Your subscription will update immediately according to the new plan.