I've come across soething today that I've not worked with before

I'm using some iframe code and looking at it in my page it is appearing as a small box with scrollers on.
I would like it to appear in the whole page.
How does it work with these iframes and why is it showing as a small box.

Salafi BookShop Cardiff Live Events

<iframe allowtransparency="true" src="http://salafiwales.co.uk/wp-content/themes/Chameleon/liveEvents/event.php?id=1"
frameborder="0" height="820" scrolling="no"