Only administrators are allowed to manage the network settings.
To modify your subscription :
From your profile, go to Settings
Under Organization settings, click on Billing
Click on Upgrade subscription
Select the desired number of users (in this example, we're upgrading from 70 to 80 users)
A prorated invoice is automatically calculated*.
Click on Next
Verify your billing information
Click on Next
Confirm that you have read and accept the subscription contract
Then click on Upgrade
You will receive an invoice for the added licenses by e-mail.
*The amount is calculated as follows: number of users added X price X number of months remaining until the next yearly renewal (to the day).