To delete a story, select it and choose Delete from the Story top toolbar tab.
In browser Twine, deletion is permanent. You may want to archive your story before deleting it.
In app Twine, deleted story files are moved to your trash can or recycling bin on macOS and Windows. (On Linux, Twine does its best to move the story to the trash, but what exactly it does depends on your desktop environment). If you change your mind about deleting a story, you can take it out of the trash or recycling bin and re-import the story file.