how do you delete old npc's that you create?
Currently, there's no way to edit or delete custom-made npcs. You have to break into the game files.
AppData\LocalLow\RalivDev to find where the game files are, where you'll be able to find game saves, saved appearances, and the player-made npcs. I don't know if it'll be in the same place on every computer, but that's how I found it on mine.
Hope this helps.