Training...

LST is pretty much training your plant to grow bigger and spread it over your grow space to increase yield and control it's Hight . I'd start with topping it at the point your plant is at right now, and once the new growth shoots grow bigger start bending them and tying them down to spread out it's growth and expose the nodes to more light. Wait until new growth has at least 4-5 new nodes before topping again to prevent airflow problems! Plant looks amazing though!! Hope this helps! Good luck and happy growing :)