How to unlock bootloader?

Hi guys, I am using lg g2 mini D618. With official Lg lollipop 5.0.2. However I want to get a custom recovery, so I rooted my device. Now only the boot loader is the problem for me. I tried to unlock the boot loader using the zaap method, and followed the exact same steps, However the terminal emulator on the Android said, "No such file or directory", or something similar to that. I cannot post in the Zaap forum because I'm new to Xda, So I decided to post here. So please can somebody tell me, that how to unlock boot loader easily. I would be very thankful to you! :p And one more thing, Does unlocking boot loader erase all of your data?