i gotta say, i recommend Stormwaves skin installer as its way easier and mucho more convenient than adding full themes by hand, but...
if you wanna do it manually, just put everything from the theme in the same/corresponding directory on the DStwos SD.
- plug = _dstwo/plug
- ui = _dstwo/ui/NeonGreen
- patch = dstwo/patch
- NDSGBA = NDSGBA/system/gui
- NDSSFC = NDSSFC/system/gui