boot loader unlock and root

please any body suggest me an easy way(any way) to unlock boot loader and root my device,my ultimate wish is to root my device to remove bloatware. I searched the entire forum for a way to root my device but there are lot of conflicting opinions some say unlocked boot loader is a must for root , some threads say root is required for unlocking the boot loader,i am confused ,please give some advice by witch i can ultimately root my device

my device- ZE550KL

OS - MARSHMALLOW 6.0.1
with locked boot loader and unrooted
2GB ram
I will be grateful to you and ill be glad