You need more inboxes or users? No worries, managing your plan and upgrading is easy in hints.
 
Simply navigate to your configuration settings, select "Subscriptions" in the top bar, and choose the plan you wish to edit.
 
In the "Action" column, click on the dollar sign. 
 
You will be redirected to your billing account, where you can access all your invoices, update your billing details, and upgrade your plan.
Note: To handle any billing-related tasks, you must be an Admin of the account.
 
If you're not an Admin and require access to manage your billing, you can request any Admin on your account to grant you Admin privileges.