You can restore Oracle Grid Infrastructure for a standalone server (Oracle Restart) to the previous release after a successful or a failed upgrade.

• Options and Restrictions for Oracle Restart Downgrades
  Review these downgrade options and restrictions when you downgrade Oracle Restart to an earlier release after a successful or a failed upgrade.
• Downgrading Oracle Restart
  Use this procedure to deconfigure and downgrade Oracle Restart, or to troubleshoot Oracle Restart installation errors.