With this method you wont need to download the android SDK and instead can download a small package of files that have been uploaded below, this saves around 1-2GB of bandwidth.
ADB and Fastboot Package – http://db.tt/B5vG1ynM
Firstly we should confirm your phone can be unlocked.
To check if your phone can be rooted go to the phone dialer and tap *#*#7378423#*#*.
A service menu should pop up.
Tap Service info > Configuration > Rooting Status.
If it says boot loader unlock allowed then you are good to go.
if it says not allowed or no then you will need to pay to have the boot loader unlocked via unlock-bootloader.com.
Now we need to get your IMEI to do this type in the dialer *#06# another window will appear with your IMEI number write this down somewhere as you will need it later, alternatively you can get the IMEI from under the battery.