When a new entity is created, a number of metadata and supporting system records are created for it.
You can edit an entity by editing existing attributes, adding more attributes (Data Model section), extend the data model with data extensions (Extend the Data Model section) and defining relationships.
Attributes can be deleted from the Data Model, however if the attribute has records that have been inserted by an end-user, then the records have to be deleted first then delete the attribute.
You cannot edit the following entity attributes: EntityType, Name, PrimaryAttributeName, PrimaryAttributeDisplayName, once you configure it. The Business Workflow is read-only as well, but can be changed from the Buisness Workflows menu.