Template management and generated-report management affect different records. Confirm which item you intend to change.
Do not assume uploading a similarly named file overwrites the existing template. Previously generated reports remain snapshots.
Use its delete action on Document Templates, review Delete document template?, and confirm only when it should no longer be available for generation. Full Access and Manage Report Templates are required. Retain an appropriate source copy before removing a template you may need again.
In the case's Reports tab, use the report's Delete action. The Delete generated report? confirmation states that its record is permanently deleted and the generated file is removed when storage cleanup succeeds. This requires Manage Report Templates.
Check your retention process and the intended case and version. Deleting a saved report does not retract copies already downloaded or delivered.