Good to have your company, Arcan. You should be able to buy or download free books from pretty well anywhere (those pre-loaded tend to be classics or public domains freely available elsewhere).
Here's a valuable tip for you. Do what thousands of us here at MobileRead and more than a million other ebook readers around the world swear by. Download free Calibre Library software. Excellent and just what you need to use your device to its best advantage. You can get the download here:
http://www.calibre-ebook.com.
Happy e-reading and best wishes. Neil