iBooks needs no introduction if you are using an Apple iPhone. You might not only use it for reading eBooks but also for displaying and checking out PDF files. The application has been updated to version 1.5 and adds a lot of new features.
Probably the most important two additions are “nighttime reading” (a theme easy on your eyes for reading in the dark) and “full-screen layout” (that allows you to maximize the content of the book and read without distraction). There are also some new fonts added (Athelas, Charter, Iowan, and Seravek) as well as a redesigned annotation palette. Follow the source link below to update or check with your iTunes/App Store applications for the refresh/installation.
Source: iTunes App Store