Instructions
Look for the "Size" button on the book page on the e-reader's screen. It's the plus symbol within a circle icon with a mark protruding from the circle at about the five o'clock position. The "Size" menu will appear.
Press "M," "L," "XL" or "XXL" and the text size will change. The text and layout will be adjusted to fit the screen and the selected size will be indicated in the bottom left corner of the screen.
Check the e-ink text's increased darkness. A good letter to look at is a capitalized "E." Look at the vertical stem, the three horizontal bars and at the serifs. The larger sizes will appear darker because they are using more e-ink microcapsules. Microcapsules are a bit like the pixels that you see on a computer screen. Press "S" to return to the original size and darkness.