Wizzard1,
Your player is quite specialized with a 128x96 screen so I do not recommend trying to upgrade your firmware it is the fastest way to trash your player.
Try extracting the firmware with s1fwx and then using s1res to change the theme, there are guides to doing this in the Knowledge Base and all the apps are in the Downloads>Tools section.
It is possible to add or replace memory chips but my understanding is that you can not go above 2GB. There is a guide at the s1mp3.org wiki here
http://wiki.s1mp3.org/index.php/How_..._a_memory_chip.