If changing icon inside of the source code and rebuilding it doesnt solve it (changing the exe icon) you can use tools like resource editor to do it. Keep in mind that icons are cached on the computer, meaning that if you already have an exe with the same name and different icon, in the same location it wont update until the computer refreshes that cache( it will appear to not have changed), to properly test you should either rename the exe file, move it, inspect its properties (the icon should be updated in the preview) or change the view size of the icons on the desktop ( if exe is on the desktop)