I got a used LG K4 off eBay and I'm looking to flash a Marshmallow ROM. I tried downloading the SuperSu ZIP file and booting into recovery, but the only option was factory reset.
I rebooted and tried Kingroot, because you don't need to boot into recovery for it to work. It didn't work, it just said 'Root failed'.
I did some research and found out that you need to unlock the bootloader. I didn't know this because on my previous phone the bootloader was already unlocked. I searched on how to unlock it on my device but all the suggestions just told me to boot into recovery.
Is there a good way to manually unlock the bootloader? I have a raspberry pi 3 and my mother has a Windows 10 laptop, so either can work. Thanks!