It is there in the read me...
Apply to your entire system
(Warning! The following method involves changing DLL files in your Windows directory. Do not use this method unless you are comfortable making potentially breaking changes to your system and you understand the consequences, including the security implications. Proceed at your own peril!)
If you want to affect the order of controllers for your entire system, that can be accomplished with the following:
Create a System Restore Point, just to be safe
Fully quit any applications that make use of DirectInput. (They cannot be running in the system tray.)
Open your system32 directory, usually C:\Windows\system32
Take ownership of the file dinput8.dll and change its permissions so that the Administrators group has full control of the file. I'm not going to provide instructions here as you can use your favorite search engine to figure out how to do this. If you're not comfortable taking ownership of a file then you probably shouldn't be tampering with your Windows directory!
Rename dinput8.dll to dinput8org.dll
If your Windows installation is 64-bit, copy x64/dinput8.dll from the release directory or release zip file into system32. If your system is 32-bit, copy x86/dinput8.dll into system32 and skip to step 11.
Open your sysWOW64 directory, usually C:\Windows\sysWOW64
If you're using TrackIR, to prevent it from crashing, copy the original dinput8.dll from sysWOW64 to the TrackIR directory. If you're not using TrackIR then you can ignore this step.
Take ownership of dinput8.dll and change its permissions so that the Administrators group has full control
Rename dinput8.dll to dinput8org.dll
Copy x86/dinput8.dll from the release directory or release zip file into sysWOW64
Copy devreorder.ini to a folder named devreorder located in your program-data directory, usually C:\ProgramData\devreorder\devreorder.ini
Edit that copy of devreorder.ini as per the instructions in the above sections