While you can increase the font size and change the text from one column to two, your book won't fill the entire screen like it does on a Kindle device. Of course, you can make the app or the web browser full screen, but the book still won't take up the full screen. The Kindle desktop app will fill the page more than the browser will. If you want to increase the size of the page tap on the Aa icon at the top. Then, select the Single column option. If you want to increase the size of your book on the Kindle Desktop app tap on the Aa icon. Then, move the slider next to Page width to the right.