Imagine a dresser full of clothes. Whether you were on the moon or on Earth, the mass -- or amount of "stuff" in the dresser -- would remain the same. Kilograms are a unit of mass. Conversely, the weight or the pull of gravity on the dresser would change if you were traveling in space. Weight is measured in Newtons and is equal to mass times the acceleration of gravity. Because the acceleration of gravity is a constant 9.81 m/s on Earth, you can convert Newtons to kilograms with simple division.
Doing the Math
One kilogram is equal to 9.81 Newtons. To convert Newtons to kilograms, divide by 9.81. For instance, 20 Newtons would be equivalent to 20/9.81 or 2.04 kilograms.