Step 1. Download minimal ADB FASTBOOT, link here.
Step 2. Unzip adb fastboot.zip, open the folder and in the free space of the folder press
Shift, Right click and choose to open a comand window. You can also go to Widows Search, type cmd and right click run ass admistrator. Then type cd /(the path ot the adb fastboot folder) or cd and drag the folder.
Step3. Go to your device Settings->About Phone->Builde number and tap it 5-6 times to enable developers mode. Then go to Settings again and enable usb debugging. Connect your phone to the your PC(installe the drivers).Now type to the cmd window adb devices. A message like this will appear at last type adb reboot bootloader and a small message will appear at the bottom left of the screen.
If you have any problem like this, try to reboot your phone and when it is booting type adb reboot bootloader.
Step 4. You must fined a custom recovery.img for your device, go to google and search. Download the custom recovery.img and put it in the adb fastboot folder. Now type at the cmd window fastboot flash recovery recovery.img. If your recovery image has a defernt name type the name.img like the fastboot fash recovery name.img. Also you can type fastboot flash recovery and the drag the recovery.img from where you have downloaded to the cmd window if you don’t want to place the recovery.img to the adb fastboot folder.
Step 5. Type fastboot reboot and let your phone reboot. You can access the recovery by pressing volume down+up and the power button in my Lenovo K3 , you can also press volume down, home and power button in other devices.
Step 6. To root you device you must download SuperSu image from here and then put it on for SDcard. To installe SuperSu you must access the recovery and then go to install zip from exeternal SDcard. You can aslo install a diferent rom for you phone. To change rom you mast download a custom rom.img for you device and the open gapps, go to google and search. You must have the open gappsbecause without them you will not have any google service. Install the rom.img then the gapps.img and last SuperSu to have root access.