I'm just wondering, I saw some in the net, is it true that I can change the theme of my NDSL?, how? and where to download?
You must be talking about the on screen skin? Not to the NDSL's console software. You can do so by changing the "interface skin" in your flash cartridge. Where to download? It depends again on what flash cartridge brand you got. Not all flash cartridge brand can have its interface skin changed. Most R4 and SuperCard can.