jaisbell, most important point. Never Ever "update" or "upgrade" with someone else's firmware file. It will very likely kill your player.
What i'll suggest is to extract and repair your player's current firmware
http://www.mympxplayer.org/how-to-ex...tool-vt66.html
Keep this as a backup and another copy for theming.
Next to theme your own firmware, the guide is
http://www.mympxplayer.org/how-to-mo...ool-vt206.html
You'll need to swap each individual images manually.
Finally when done, re-flash the editted firmware back, guide is
http://www.mympxplayer.org/how-to-up...ayer-vt46.html
It is always adviseable to theme using your own extract firmware, as it is safer rather than using someone's themed firmware.
As for opening your player, there should be a few catches between the front and back casing. Wedge a thin screwdriver or knife between and locate the catches. Then apply slight pressure to release the catches. However there is a risk of breaking the catches in the process.