The firmware file must be in the root directory, not a folder.
For a visual walkthrough on navigating the Toshiba settings menu and initiating an update, watch this step-by-step guide: toshiba tv firmware update usb verified
Finding a "verified" file is the most challenging step. Here's where to look, in order of safety: The firmware file must be in the root
Document version 1.0 – For technical support and field engineering use. toshiba tv firmware update usb verified