You can either upgrade or downgrade to a different plan as you like. However, any change of plans will only be activated by Apple App Store / Google Play Store only at the end of the current period.
If you want to change or switch your subscription immediately, here is what you need to do:
Request for a refund from Apple or Google Play
- Subscribe again on the Phoner app.
For iOS Users:
On your iPhone or iPad
- Open the Settings app.
- Tap your name, then tap Subscriptions.
- Tap on the active Phoner subscription.
- Tap on "See All Plans"