When creating a new Aiven service, you are not tied to a plan. Your services can be adjusted to better match your needs. Services can be moved to a higher or lower plan, and to a different tier—Startup, Business or Premium.
Go to your Services, and open the service you want to scale.
On the Overview tab, scroll down to Change Plan.
Select the new service plan and new tier, if required.
Your service will be in a Rebuilding state, and once complete will be on the new plan. The service will still be accessible through the process.