How to modify private static variable through setter method

I have the following variable in a class named Example:

private static int number;

If I wanted to assign the variable a number using an outside class, which would I do?

1) Make the setter method in Example static so I can access it like this:

Example.setNumber(3);

2) or Make the setter method non-static so I create an object of Example to set the number

Example e = new Example()
e.setNumber(3);

What are the differences between the two and which one is the better way?