LG G3 D858HK SOFTWARE How to update

Dear XAD Friends ,

I n Sanjeev i want to update my phone to marshmallow 6. I'm currently using Android 5.01.

I m from india it is a imported model from Hong Kong . it is rooted already.
Guide me how to upgrade it .
Software version is D858HK20D-HKGXX

PLEASE HELP ME IN FINDING SOLUTION
:o