In order to disable SSL you will need to change includes/configure.php and admin/includes/configure.php.
in includes/configure.php find the following code:
// Define the webserver and path parameters
in admin/includes/configure.php find the following code:
Make the changes indicated by the highlighted text.
IMPORTANT NOTE: Remember, your configure.php files are probably marked read-only. You'll need to change them to read-write in order to upload your updates, and then put them back to read-only. See the FAQ on setting file permissions.