In Settings > General, I change my site to be
https:// and now when I go to
/wp-admin I get a 404 Not Found.
Is there a way I can revert this? I tried Googling but found nothing :(
You cannot revert this. You will need to export your database via PhpMyAdmin and find all of the "HTTPS" instances and replace them with "HTTP". I would suggest using something like Dreamweaver or Notepad++ to 'find and replace all'. After you have done that, import your database again.