1. Click on the gear icon, choose settings
2. Open the Sales documents
3. Choose the Order from which you would like to remove a custom field information
4. Find the custom field that you want. Uncheck the box next to the Mandatory field. Click on the Save button and then click on the X next to the field you would like to remove (example D.)
5. After you click on the X to remove the file, click again on the Save button.
6. When you remove the field, check the box next to the Mandatory field again and click on the Save button
After you follow all the steps, the field you want to remove will be deleted, and the question that you have as a Mandatory will remain Mandatory in your account.