When you want to globally replace fonts used in a QuarkXPress Layout, you probably already know to choose Utilities> Usage.
But here are a couple of things you may not have known:
You can simultaneously replace multiple fonts in the list with one new font. The trick is to hold down a modifier key as you click to select multiple fonts in the list. To select multiple fonts that are next to each other, hold down the Shift key as you click the first and last font you want to include.
To select fonts farther up or down the list, but skip the ones in between, hold down the Command key as you click on them (Windows: Ctrl):
If you want to see technical details about exactly which font is being used — and its location on your computer — just click the little disclosure triangle in the lower left of the Usage dialog:
That takes care of the fonts in the current Layout. If you want to replace fonts in another Layout, switch to that Layout and repeat the process.
None of this affects the fonts on Master pages. To replace fonts on a Master page, you need to display each Master page and repeat the process. Fortunately, QuarkXPress 8 has a handy button at the bottom left of the Layout window that lets you toggle between a page and its Master page: