By Windows explorer, which you should already know as you already extracted the game. But you need to enable hidden files in "View" tab, in order to be able to see Appdata, which is hidden folder.
Ah good call, I didn't think about hidden files.
You can also manually enter the path into Windows explorer by copy-pasting the path Reginald gave.
The savefile will be named 'savedGames.gd'.