You can manage your subscription anytime through your Apple ID settings. If you change your subscription tier, you'll be refunded for any days you have left on your current subscription and will then be charged the new subscription price through your Apple ID.
You can find more information on how to manage your subscriptions here: https://support.apple.com/HT202039
Currently, it is not possible to change the subscription plan during a running trial or subscription.
In order to switch to a different plan, you will have to cancel your current trial or subscription first directly within the Google Play Store. You can find more information on how to do this here.
Once your current trial or subscription period expired, you can then resubscribe to the desired plan within the IDAGIO Android app.
If you need further assistance, please send us an email to "firstname.lastname@example.org".