Question

How can you make gravity smaller and bigger

Answer 1

You can increase the forces of gravity between you and,
let's say, a planet, in two ways.

Way #1:
Increase your mass. 
(Eat or drink more.
Fill your pockets with rocks.
Put on a heavy coat or space suit.)

Way #2:
Get closer to the center of the planet.
(That only works down to the planet's surface, but
it stops working if you go below the surface.)

To decrease the forces of gravity, do exactly the opposite:
-- lose weight
-- get farther away from the object that gravity is attracting you to .

Also, don't forget: 
The forces of gravity always work both ways. 
The less the planet pulls on you, the less you pull on the planet.
The harder the planet pulls on you, the harder you pull on the planet.

Answer 2

The force of gravity = GMm / r^2, where G is gravitational constant, M is mass of one object, m is mass of another object, r is distance between them.

To make gravity smaller, decrease mass or increase distance.
To make gravity bigger, increase mass or decrease distance.