This is the simplest method. Your TV will communicate directly with TCL's servers to check for available software.
If you encounter issues after the update, consider doing a factory reset. Tcl 55c2us Firmware Update
The screen should show an upgrading note. Do not turn off the TV during this process , or you may damage the system. This is the simplest method
If your TV is stuck or the standard menu update fails, you can perform a "forced" flash: Tcl 55c2us Firmware Update
Ensure the drive is FAT32. Rename file strictly to Update.zip if requested by instructions. Use the USB 2.0 slot rather than the blue USB 3.0 slot. Corrupted download file.