Hi there, thank you for contacting us!
Here is the detailed instruction on how to change your subscription plan in Google Play:
Open the Google Play Store app.
Tap your profile icon (top right) > Payments & subscriptions > Subscriptions.
Find Invoice Maker in the list and cancel your current subscription.
After cancellation, go back to the Invoice Maker app.
From the app, start a new subscription.
That’s it! Your plan will switch once the current billing period ends. Let us know if you need help!