Increase iframe height in parent

I have site A that has an iframe and site B shows up in this iframe. I need to increase the height of the iframe according to the content in it from inside site B. I need some pushing in the right direction to get to some documentation or online resources.

Thanks

Within an iframe you can access the parents document through the parent object e.g.


parent.document.getElementById('iframe-id').style.height = '500px';

Thanks.