Hi David,
Looks like you are using Ariba Administration UI to configure fields. If you are using a on premise solution of Ariba, you will have an option in customization manager to download the AML file and clean the field and upload the file back and restart the server for changes to take effect.
In case you are using a On-Demand solution, you will have to submit a service request from connect.ariba.com and they will help you if there are no dependencies. Also, you should refrain from creating fields that you are not sure you need as all these fields that you create can only be soft deleted.
Regards
Vilas