setfont word 

Sets the font for the selected text in the current text box. If no text is selected, setfont sets the cursor to use that font for typing. The input must be the name of a font in your system.

Example: 

setfont "geneva
print [Hello there]

The next instructions select all the text in the text box and set its font.

top
select
bottom
setfont "monaco
unselect