Navigate to the Appexchange – This can be accessed from your force.com app menu in the top right-hand corner in classic view.
Log in using your Salesforce login credentials and navigate to My Account.
Locate RIO Inventory in your list of installed applications.
Click on Modify Subscription and update the number of Users you need – any charges for additional Users will be pro-rated to match your current subscription period.
Assign the relevant Users access to RIO inventory by following the documentation.