Download Nexus Root Toolkit 1.9.9 from here, here or here. You can downlod previous version of Nexus Root Toolkit 1.9.8 from here.

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

VERSION 1.9.9 - 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. This release brings Lollipop support, bug fixes 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
· Nexus 9: HTC Wifi Tablet
· Nexus 6: Motorola 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 1.9.9: November 26th, 2014
· New feature for flashing a build specific ‘No-forced Encryption’ boot.img [for Nexus 6 & 9]: Advanced Utilities > Fastboot Flash > Boot > ‘No-Force Encrypt’ button
· Root method no longer relies upon root_kernels, but rather utilizes Chainfires latest and greatest SuperSU.
· Added a dedicated ‘Vendor’ button in advanced utilities for flashing that image on the Nexus 9.
· Added new Fastboot Erase and Fastboot Format features (advanced utilities), which allow users to perform batch wipe operations after selecting the partitions with checkboxes.
· Added new ‘OEM Device Info’ button in advanced utilities ‘Quick Tools’
· Re-organized advanced utilities into top-level blocks ‘Fastboot Flash’ and ‘Fastboot Boot’ respectively; so previous features like ‘Restore Stock Recovery’ can now be found in a sub-gui after hitting Fastboot Flash ‘Recovery’ Button.
· Restore Stock Kernel script no longer performs a temp boot test operation, it just flashes it.
· Flash TWRP/CWM/PHILZ/OTHER scripts, now allow you to disable the additional operation of flashing ‘perm-recovery-signed.zip’ which is only needed the first time you flash an alternate recovery (so for example if you are just upgrading to a new version of TWRP, you can forgo flashing that zip and just have NRT flash the new version).
· Fastboot device detection now auto-retries to connect once if it doesn’t the first time.
· Updated the included adb/fastboot binaries to the latest platform-tools release from the SDK
· Added an automatic check to see if ‘Bluestacks’ application is running on start, to ask the user if they want NRT to close it (because this application causes conflicts with NRT)
· Bug fixes to multi-updater to deal with scenarios where not all files are available for a device yet (like TWRP currently for Nexus Player)
· Minor bug fixes, code optimizations, and feature enhancements.

via www.wugfresh.com