Steps to unlock bootloader of OnePlus 2
1 .Download and install ADB and Fastboot
2 .To unlock the bootloader first put the smartphone in fastboot mode. To enter Fastboot mode, press and hold the Power button + Volume Up continuously You will see Fastboot mode written on your OnePlus 2.
3 .Now connect your smartphone to PC using a USB.
4 .The next thing which you need to do is open command prompt window. In order to open command window press windows+R to launch the run menu,in run type "cmd" to launch the command prompt.
5 .After opening the command prompt, Change current directory to the Adb and Fastboot downloaded directory like cd c:/Adb
6 .After changing the directory to adb and fastboot,Run the final command to unlock the bootloader of OnePlus2
fastboot oem unlock