Dynamically populate a select field’s choices from a select field

I have a select field that have 4 values.

Value 1
Value 2
Value 3
Value 4

When the User selects one of these, I want to load the sub select field of that parent, so if I choose Value 1 I want a different select field too show up and to be chosen from.

Subvalue 1
Subvalue 2

How can I create a subselect field and how to add values and connect it to the first selection?

I read some about dynamically loading, but I’m not sure how to do it.

http://www.advancedcustomfields.com/resources/dynamically-populate-a-select-fields-choices/