如何刷新模态中显示的字段

Im sure this is a very basic question, but i'm stumped! I have a modal that appears fine and what im trying to do is once a value from a dropdown is selected, have different fields appear depending on what option was picked! I know how to get the value and i intend on sending that value to a javascript method which determines what option was selected. What i don't know is how to get different fields to appear on my modal depending on the selection.Im sure this is a very basic question, but i'm