Is my data stored if I upgrade/downgrade my subscription plan?

YES, your data will still be stored even if you upgrade or downgrade your subscription plan.

If you upgrade, you will gain access to additional features available in the higher-tier plan;

If you downgrade, you will only have access to the features and limits of your new (lower-tier) subscription. Any functionalities exclusive to the previous higher-tier plan will be disabled, but all your existing data will remain safe and secure.