how to increase image size in iPhoto 9

I am used to using Microsoft Picture Editor (or at least Paint) to just increase the size of an image to a percentage over 100% or a specific pixel size. I understand it makes the picture somewhat grainy in theory, but taking a tiny cell phone pic and making it viewable on a large screen requires the image to be bigger. I can't seem to find a way to do this. Exporting doesn't seem to help either, unless I'm missing something.