How to downgrade the Sony PRS-T2 firmware?

Hi! Thank you very much for reading this.

I have a Sony PRS-T2. It was updated to the latest firmware (1.1.00.17210), so I cannot root it.

I was wondering if you knew any way in which I could install an older firmware version so I can be able to root it. I have tried a factory reset, but it doesn't work.

:thanks: