How to disable/delete a brand?
As brands are attribute options, you will need to delete the option from the Brands attribute. For that, please go to Stores → Attributes → Products and select the attribute that is set as brand in the general extension configurations. In the Properties tab, you will find a list of attribute options:
On the right side, there are two buttons — for configuration and for deleting the attribute option. Deleting the option will delete a brand from all store views.