Clicking the Manage Entities button will open the Entity Manager window:
The Entity Manager lists all Entities currently in the Maltego client and allows you to edit or delete Entities.
Clicking the Delete entity button will open a confirmation dialog box before the Entity is removed:
Clicking the ellipsis button on the right of the Entity line item will open another window that allows you to edit the Entity:
From the Entity editor window, you can change any of the settings and properties that were made to the Entity when the Entity was first created.