You need only one of the four engine files. The four executables are
compiles of the same source code for different CPUs. They differ in speed only; sorted in descending order these are: stockfish_8_x64_bmi2.exe, stockfish_8_x64_popcnt.exe, stockfish_8_x64.exe, stockfish_8_x32.exe. Keep the fastest which runs on your system and delete the other three.
I loaded the four engines to Arena, but it always says at the top (2000), which means level 2000, how do I make it level 3000+?
This number doesn't set the playing strength. It has informative purposes only. You can change it as follows:
- Open 'Engine Management' (F11).
- Click the 'Details' tab and select Stockfish from the list.
- Click the 'Information' tab in the right part and type the desired value into the 'Rating' field. If this field is empty, a default value of 2000 will be used.
- Close the dialog and start a new game to display your new setting.
You can't set Stockfish to play at a given Elo level. If you want to weaken it, change the Skill Level in the engine settings (Ctrl+1, if it's loaded as 1st engine). '0' is the weakest setting and the default value '20' means full strength.