You have to decompile it and some other things... I'm not that experienced with C++ so I can't tell you for sure, but I do believe that's what you have to do. You'd have to decompile and then find the original code for it, and then edit that code, and then make it a .exe file again.
Disclaimer: I'm not pro at C++ or any of those, so this is just based on what I know.