Clicking the Manage Entities button will open the Entity Manager window:
The Entity Manager list 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.