Yes. You can move to a higher or lower plan — including back to Free — from inside the app, and the change is instant. To stop all charges, move to Free or uninstall the app.
When you move to a lower plan:
charges already made this cycle aren't refunded;
your action count for the cycle stays as it is — if you've already used more than the new plan allows, new runs wait until the cycle resets.
Not sure which plan to move to? Chat with us first.