Your subscription to the service can be managed via the ‘Subscriptions’ page, allowing you to;
View your existing # users which contribute to your subscription
View the history of users which contribute to your subscription -
Switch to a different plan - either up, or down
Register or change your credit-card details
View and manage any add-ons you have requested (in addition to any which may be included in your selected plan)
Subscriptions are billed on a monthly basis in advance (eg. for the next month), for the amount shown on your selected plan.
Plans
Each plan caters for a certain number of active people (people whom haven't been archived or removed).
You can change your plan at any time, either up or down.
Some plans may come with additional facilities that others do not (eg. larger plans allow for groups to be setup in order to manage the larger numbers of people, whereas this is generally not available on smaller plans, in order to minimise the additional complexity)
Add-ons
Add-ons may be available to enable via the ‘Subscriptions’ page as well - their availability, complexity and pricing varies on a case-by-case basis.