pele, what version is your player's firmware? If it is v3.5.35, v3.5.37 or v9.0.43, then you can change the themes. Any other versions are not yet supported.
First extract your existing firmware using S1fwx, guide here
http://www.mympxplayer.org/how-to-ex...tool-vt66.html
Next, using S1res, you can theme your player, guide here
http://www.mympxplayer.org/how-to-mo...ool-vt206.html
There are many theme packs that you can download from the downloads section. But don't flash the firmware file downloaded directly from the site.
Rather, use their images and swap with those in your extracted firmware.
Finally, re-flash the edited firmware back, guide here
http://www.mympxplayer.org/how-to-up...ayer-vt46.html