Yes. You can switch between Growth and Unlimited on the Plans page. The change takes effect right away: Shopify replaces your previous subscription with the new one, and a new trial doesn't start. Any credit for the unused part of your previous plan is handled by Shopify under its usual rules for plan changes.
If you move from Unlimited to Growth, your view counter starts from zero with a full 20,000 views and a new 30-day cycle.
There is no free plan to move to — development stores are the only free option. To stop all charges, uninstall the app. Shopify cancels the subscription and pop-ups stop showing right away. Your pop-ups, subscribers, statistics and integrations are kept, so if you come back, everything is where you left it — you'll just choose a plan again.
Not sure which plan to move to? Chat with us first.