Have your needs changed? You can change your plan at any time.
Key points 
Move up to a higher plan (more features) or a lower one
Choose monthly or yearly billing
You can enter a promo code at the time of payment
The change is handled automatically by Stripe (with prorated adjustment)
Moving up to a higher planIn the Subscription section, choose the plan you want. Access to the new features is immediate after payment, and billing is prorated by Stripe.
Moving down to a lower planYou can also downgrade your plan. Remember to check that your usage fits within the limits of the target plan (number of galleries, storage, features).
Using a promo codeAt the time of payment, a field lets you enter your promo code: the discount is applied automatically.
Where do I enter my promo code? On the payment page, when subscribing or changing plans.
Is the change immediate? Yes for an upgrade; billing is prorated.
What happens if I downgrade but I exceed the limits? Check your usage first: beyond the limits of the new plan, certain actions (creating a gallery, adding storage) will be blocked.