Display Content Without Reload

I have a CMS, and the user is able to choose from 3 different layouts on their website by using a drop-down menu.

What I am wanting to do is have different form elements appear (whilst keeping any text they have/haven’t submitted) after the user has selected an option without reloading the page.

I have seen this done. Guessing AJAX. Can someone point me in the right direction for this one?