Can I upgrade/downgrade my purchased add-on to another tier?

NO, you can't.

Each membership tier has its own exclusive add-ons and pricing. If your current tier is Launch, you can only purchase add-ons that belong to the Launch tier. Add-ons from other tiers are not available unless you upgrade to that specific tier.

In short, you can only purchase add-ons that match your current membership tier. If you require more features, please consider upgrading your membership tier first.

If you want to upgrade or downgrade your add-on, you must first upgrade or downgrade your main subscription plan. You may read How to upgrade/downgrade my subscription plan? if necessary.