yzn , most important thing, Do Not upgrade your firmware. You will most likely brick your player.
However, you should backup your original working firmware, the guide here
http://www.mympxplayer.org/how-to-ex...tool-vt66.html
To theme to your player, use your extracted firmware and by using S1res tool, you can theme the firmware. The guide is here
http://www.mympxplayer.org/how-to-mo...ng-vt1719.html