You can change the font, the size of the text as well as the paper layout in iBooks. Check out the article below for answers to other questions that you may have.
Can I change the appearance of my books?
Yes, iBooks allows you to adjust the font size and choose from five included fonts. You can also select sepia-colored pages and text and adjust the brightness of the device's display to make your books comfortable to read in any lighting situation. You can select the Night option in the Theme section within iBooks to read books in the dark. You can also change the appearance of books by changing the contrast setting on your iOS device to display white on black. On your iOS device, tap General > Accessibility and toggle the setting "White on Black." Then, open iBooks to read books with white text on a black background.