Each quarterage is defined as a "Plan" within Outseta. To edit your plans go to Billing > Plans.
When the price of a plan is updated, any members on that plan will pay the adjusted yearly rate on their "Renewal Date". The price can be updated at any time but be aware that new users who subscribe after the price change will start paying the new pro rata amount immediately. It is recommended that the prices change as close to the annual renewal date as is acceptable. A discount code can be created for new users to mitigate this situation between the time the price is updated and the renewal date.
In the event of a price increase, it is advised that at least one email campaign (Email > Broadcast) is scheduled to alert the member base of the upcoming change(s).