To update your Mobile Connect lisences, do the following steps:
Navigate to the "Manage Subscriptions" page in AWS Marketplace
Look in the table for "Mobile Connect" and click on the Agreement ID.

Click on "Actions" > "View terms"

Look for the option to "Edit agreement", which is usually visible in a blue banner box

Update the license amounts how you see fit and save changes.

If you have problems during this flow, don't hesitate to reach out to mc.notifications@ideal-systems.com