The Casio fx9750 to fx9860 files used in order to flash the upgraded operating system onto the calculator.

Version number can be found on the system section of the main menu.

If your fx-9750 calculator's version number starts with 02.00 or 02.01, use 2_01_0200_sh3.fls . 

If you have 02.02 at the start of the version number(or a USB Power Graphic 2), you need to use 2_02_0201_sh4.

Look up a tutorial to upgrade your calculator. Other software is needed but these files aren't easy to find