The only legitimate way to lower your firmware is through a complex hardware process known as . However, even this method has strict limitations:

You can generally only revert to the previous firmware version that was installed on your console before the 13.02 update. For example, if you updated from 12.52 to 13.02, you can only go back to 12.52.

To go all the way back to 9.00 from 13.02, your console must have sat on firmware 9.00 immediately before you updated to 13.02, without any intermediate updates (like 10.00, 11.00, or 12.00) in between.