PS3 DEX 4.21 - Play original BD 4.31 games

Hi everyone.

This is my first post, and a really need your help. I've already tried to search the web for a solution, but with no luck.

I have a PS3 with DEX 4.21 installed. And because I'm a fan of the Tomb Raider series, I've bought the original game (4.31). But I can't play it. It says that requires the new update 4.31 but can't install it.

Can you tell me what can I do to play original Bluray games that require 4.31 updates?

Please help.

Thank you all.
Regards,
Nux