First of all just download Nexus Root Toolkit 1.8.9 from here, here or here.
You can downlod previous version Nexus Root Toolkit 1.8.8 from here.

Unlocking, rooting, relocking and unrooting simplified! (and much more!)

VERSION 1.8.9 - This program will automatically bring together all the files you need to unlock and root your device in a few clicks, or flash it back to stock and re-lock it. You can also use this program to backup/restore all your important data, flash zips, set file permissions, push and pull files, install apps, generate logcats/bugreports, and much more! With the included file association options, you can perform tasks like flashing zips, installing apps, restoring android backup files, and flashing/booting img files with just a double click! The program includes a full featured interface for automating tasks in TWRP, enhanced restore features, an in-built auto-updater/notification system, ‘any build’ mode, advanced restore features,’NRT- Live Log’ for viewing the adb/fastboot cmds that are run in the background, quick tools utilities, and tools for taking screenshots/screen-recordings. All the latest Android builds and Nexus devices are officially supported including the new Nexus 5, with full KitKat support for all the newly upgraded devices. The program intelligently and selectively downloads the files it needs for your device and makes sure you are using the latest files available. The program can even auto-detect your device and build. The main changes in this release are full 4.4.4 support, improvements to the updater, and general code enhancements and optimizations.

Supported Nexus devices:
· Galaxy Nexus: GSM Models (both yakju and non-yakju builds)
· Galaxy Nexus: CDMA/LTE Verizon Models
· Galaxy Nexus: CDMA/LTE Sprint Models
· Nexus S: Worldwide, i9020t and i9023 Models
· Nexus S: 850MHz, i9020a Models
· Nexus S: Korea, m200 Models
· Nexus S 4G: d720 Models
· Nexus 7: Asus Tablet
· Nexus 7 3G: Asus Tablet
· Nexus 7 v2 (2013): Asus Tablet
· Nexus 7 v2 (2013) LTE: Asus Tablet
· Nexus 10: Samsung Tablet
· Nexus 4: LG Phone
· Nexus 5: LG Phone

Instructions:

1. Select the correct device and build (what you are currently running)

2. Configure your drivers if you haven’t already using the driver guide (If you aren’t sure use Step 3 of the driver guide to test your drivers).

3. If you need to, backup your important data.

4. Unlock your device

5. Root your device

6. Enjoy! ^_^

Learn more about each option by mousing over the control, dynamic tooltips will provide you more information, also each button displays a message about what it does first.
So the best way to get familiar with the toolkit is simply to press the buttons and read what it says.

What’s new in Nexus Root Toolkit 1.8.9: October 17th, 2014
· Revisions to perm-recovery-signed.zip to ensure it doesn’t interfere with root
· Redesigned entire dependency downloading system. No longer is the user prompted with numerous “Such and such file is not found in the local directory, press OK to download”, but rather there is a unified and dynamic interface for managing all required files/downloads per toolkit operation.
· The two exe’s for managing downloads in the past “nexwug_DL_NRTfiles.exe” and “nexwug_DLnX.exe” are now consolidated to one hybrid downloader “nexwug_downloader.exe” which manages all downloads, hash-checking, and factory pack extraction operations.
· Manual input for hash-checking is now only shown for files the toolkit doesn’t already have in the masterlists.
· Automatic hash-checking is now also performed in files that are manually imported into the toolkit via the manual download interface (when/if server issues cause the automated downloader to fail)
· Multi-device auto-update management has been revamped and redesigned, with new dynamic information displayed in the tray menu item that appears during the process. Fully integrated to work with the new hybrid downloader.
· New double-check automatic device detection (can be disabled in the toolkit options) that quickly checks to see if your selected device is correct. If the toolkits auto-device detection determines that you selected the wrong device it automatically notifies the user and asks if you want to correct the selection.
· Live-log is now governed by a quick toggle menu item in the main interface and also linked to the hotkey [ctrl+L]
· Options menu has a ‘Reset to defaults’ button now
· Drag and drop behaviour in the ‘Flash zips’ interface for reorganize zips to flash has been fixed.
· Fixes to enhance how NRT handles factory images it doesn’t know about yet.
· Major code revisions to the entire codebase in preparation for porting this kit to new devices.
· Android 5.0.0 Lollipop Developer Preview added for easy flashing and other operations (Root will not work with the current 2.13 SuperSU)
· Some message boxes specific to this last LP preview release and the infobox about root not working with SuperSU 2.13.
· Lots of other code changes implemented for general optimizations and improved user experience.

via www.wugfresh.com