Playing stockfish level 3000 on Arena 3.5.1 I downloaded Arena 3.5.1, and then downloaded stockfish from https://stockfishchess.org/ it had 4 files: 

stockfish_8_x32.exe
stockfish_8_x64.exe
stockfish_8_x64_bmi2.exe
stockfish_8_x64_popcnt.exe

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+? 

Also when I am playing on Arena, it takes 15 seconds and more for each step from the computer to play, is this right? 

Thanks, am still new to all these things.
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.