To make sure you get the exact right file, could you tell me:

Are you looking to update for or just to fix it?

Do not turn off the power during the update process.

Usually, the file is placed on a FAT32 formatted USB drive, which is then plugged into the TV, and the power is cycled while holding the power button or menu button to initiate the loading process (sometimes known as MstarUpgrade.bin or similar).

42.5" Toshiba 43U7750 - Specifications - DisplaySpecifications

If it's for a fix, I can try to help you narrow down the best version of this firmware.