How do I get my save file of Pokemon Diamond off the Cartridge, onto my computer, and back onto the cartridge?

I have Pokemon Diamond cartridge for the Nintendo DS. I want to use Pokesav to edit my file on my DS cartridge, but I am confused on how to get my file off of the cartridge, onto my computer, and back onto the cartridge.|||your gonna need a ds cartridge adapter i dont think they sell it in the u.s. though|||buy action replay and use the 999 rare candies cheat to level them up