u got to put them in ur top left hand side on screen...u wil see 4 squares...click one and it will let u pick a boook....some have times others are permant....as long as they are in there they will work for ya
To unequip a book, simply click the target and then the book interface should appear. On the first page at the top left of the list should be a grey circle with a line through it. Click it to unequip the target book. However, some books cannot be unequipped for a certain length of time directly after equipping e.g the Book: Peak Oil - A Survivors Guide, directly after being equipped, cannot be taken off for 2 days (permanent versions only).
There should be 4 squares with book icons on them underneath you XP and Level bar. just click any of them and a window should come up. The first option, an icon with empty space and a 'no-entry' sign on it (red circle with red line through it' is the one to unequip your current book.