rock-star_79, Never try to load another firmware to your player there is a 99.9 pecent chance you will brick it. You can find out your firmware version in the players settings menu under Firmware Version. If it is a 9.0.48 or 9.0.50 version then you will not be able to extract it from your players and mod it as there are no tools available for these versions yet. Any other versions should be ok.
To mod your firmware You need to first extract your firmware from your player using s1fwx.
Download
HERE
Guide
HERE
Then you can change the images using s1res
Download
HERE
Guide
HERE
If your player has a 2.0 inch screen then you will need this version of s1res
HERE
Then reload your firmware to your player using MP3 Player Utilities Update Tool
Download
HERE
Guide
HERE
There can be a huge amount of difference between firmware images and layout so not all themes you find in the download section will be compatible with your firmware. You will most likely have to create your own images or edit some of the existing themes to suit your player.