Ok if you want to revert
What you need is fresh copies of the old wordpress install files
You can find that here http://wordpress.org/download/release-archive/
YOU WANT TO KEEP YOUR wp-config.php file
Then you need to delete everything except your them folder and plugins.
Don't just copy over the files .. you should delete them and upload your fresh old copies of wordpress.
Then if it works you are fine.
If it causes database problems then you need to restore your old database from a backup.
To turn off automatic background updates