Yes. You can change the number of SDSs in your subscription at any time, on the Billing Page (More → Subscription). Only the owner of the account sees this page.

• More SDSs or a higher plan: the change starts today. You pay the difference between the old and the new price for the rest of the current period. The Billing Page shows the amount before you order, for example Amount due now for package change from 400 to 600.
• Fewer SDSs, a lower plan, or a switch between monthly and yearly billing: the change starts at your next billing date. Nothing is charged today; the new price is billed on that date.

There is no price advantage in starting with a bigger plan than you need: upgrade when your library grows. When you reach the limit of your plan, you cannot add more SDSs until you upgrade. Read more: What happens if I need more SDSs included in our subscription plan?

See the pricing page for the prices of all plan sizes.