How to change the font of my TeX editor on Mac?

In the Prefs of TeXShop, you choose the font of the source (what you see on the screen) :

And then \usepackage{fourier} or \usepackage{lmodern} or some other package in your preamble to set the font for your pdf.

Its right there in the Preferences:

TexShop->Preferences...

Top left of the dialog is the setting for "Document Font"

Yeah, I wanted a quick answer to the same question because editor font does not appear to be adjustable from the TexShop system preferences. On my mac with TexShop v 2.47,

source→font→bigger (or smaller)

work. I had to stumble around for a minutes to find that menu location, but the shortcuts are more obvious

command+equal (for bigger, b/c "shift+equal" is a plus sign)

command+minus (for smaller)

... hopefully this saves someone 4 mins of grief ...