How do I increase font size in Elementary OS luna?

The text is too small to read on the screen. How do I make it larger?

This method is  now outdated.  New method is to install OS Elementary Tweak.  Above method will still work for other distros.

sudo apt-add-repository ppa:versable/elementary-update
sudo apt-get update
sudo apt-get install elementary-tweaks

After you can find it in System settings -> Tweaks