how to root without tripping knox SM-g900F

a few months ago i tried towelroot but that didnt root, this is the first android phone ive had and have no experience in rooting so a step-by-step guide would really help including suggestions on what to do before and after rooting.

Model :SM-g900F
Android Ver: 4.4.2
Baseband: g900fxxu1ang8
Kernel: 3.4.0-2089850
Fri Sep 12 14:04:20 KST 2014

Build: KOT49H.G900FXXU1ANI4