k_thao24 , believe me i've seen 10 out of 10 cases where a firmware upgrade immediately bricks a player.
Moreover, v3.5.xx firmwares uses the ATJ2085 chipset (like you are using now). Whilst the v9.0.xx series uses the ATJ209* chipsets. Which in actual fact are 2 different chips. Although they perform almost the same functions.
However, if you insist in "upgrading" to v9.0.xx, there is an upgrade guide here, which is really just the re-flash guide.
http://www.mympxplayer.org/how-to-up...ayer-vt46.html