How to convert newton to kilogram?

These are not the same measurement of unit and cannot be converted without first measuring the gravitational field that you wish to convert in.

On Earth, the average force of gravity is about 9.8 N/kg

So 1 kilogram weighs about 9.8 newtons on Earth.
1 newton is the average force experienced by a 0.102 kilogram object on Earth.

If you need further explanation please feel free to ask :)