Is there a More button? If so, click on it, then on Format > Style

Here is the dialog box in Windows after the More button has been pressed. I assume the Mac has something similar. Where the More button was, is now a Less button.

00 deleteme 2.png

You pick the old style with the Find box active and the new one with the Replace box active.

By the way, it is unusual and probably not good practice to have all of your text formatted in one style. The only time I would do this is if I want all of the text to look the same. I usually want some of the text to stand out.