"You need to read that book."
Translation:O kitabı okuman lazım.
"Lazım" never changes I think. What changes is the gerund (infinitive -k, for example "yapmak" becomes "yapma", then you just have to add the personal possessive suffixes)
O kitabı okumam lazım = I need to read that book (word by word: "My reading is necessary")
O kitabı okuman lazım = You need to read that book
O kitabı okuması lazım = He/She/It needs to read that book