If you have a save file system using keys, then delete the keys. If you are using a document, then reset the document to its default values. If you are using the simple save/save as and load actions, then you can open a save game and reset all of the variables to what they would be in a new game, then overwrite the save. Note that all of these should only be done for the saves that you want to reset; you should not rewrite all of your saves with save/save as, you should only delete the keys relevant to your save, and you should only delete the document for the save that you want to delete, not all of them. (This is, of course, unless you want to delete ALL of your saves, in which case you should delete all of your save data - though this would also delete data "outside of" your individual save files, such as e.g., whether or not to play an intro cutscene if your game has that functionality, unless you make exceptions for that.)