How can I learn my current subscription plan and change it?

You can use your phone to check subscriptions.

To see details about your subscription status, your subscription needs to be active. If it is active then you can go to the settings on your phone.

Where is your subscription purchased from?

It is important where you purchased your subscription from. To see further information about your auto-renewal instruction status and actual subscription prices please follow the corresponding link. For iTunes and for Google Play.

Subscriptions cannot be managed or changed on behalf of the user.

The device owner needs to make the changes themselves manually. Managing your subscriptions is an external control in every device and not in the app itself.