Any time you want to change something that fundamental to a document, the
first place to look is under Tools - Options. (For this setting, look under
General - down near the bottom.)
Whenever I want to change something and see what I can change, I always
start here. Doesn't matter what the program is - they almost all have some
sort of a Tools or Settings dialog box. And as long as I don't close the
program I can tweak until I'm happy and know that I can always undo any
changes.