How do you change weight to mass?

Answer 1

You don't "change" it. Mass is mass, and weight is weight.

Mass HAS weight. How much weight it has depends on the gravity field it happens to be in.

On the surface of the earth, 1 kilogram of mass weighs about 9.8 newtons (2.2 pounds). On the moon or
on another planet, the same kilogram can weigh more, less, or the same. In an orbiting satellite, or in a
spacecraft on its way to the moon or another planet, the same kilogram weighs zero, and it floats around.

Answer 2

To change weight to mass, you need to divide the weight by the acceleration due to gravity (9.81 m/s^2 on Earth). Mass is a measure of the amount of matter in an object, while weight takes into account the force of gravity acting on that mass.

Answer 3

You don't they are the same thing.