You cannot jailbreak a ps3 on 4.31 ofw unfortunately. You need at least to be on 3.55 in order to perform the jailbreak.
Now depending on your console type, you can downgrade using hardware and mounting it inside the ps3, read about this on the ps3devwiki website.
Check the tutorials section for more and make sure to read rules and post in the proper section next time. Moved to help section, thanks.