Because this specific model (40L5400ZE) is part of an older series, official downloads may no longer be listed on the main Toshiba support site. You can typically find these files through the following community-driven platforms:
Press the Home button, navigate to Settings > System > Software Upgrade , and select Scan for update . Download TOSHIBA 40L5400ZE Firmware part4 rar
Turn off the TV, plug in the USB, and turn the TV back on. Some models will auto-detect the update. Because this specific model (40L5400ZE) is part of