In order to change the margin guides for an existing layout:
- Go to Page > Display > Master Page (for the Master Page that you want to edit)
- Go to Page > Master Guides & Grid(for QuarkXPress 8; for older versions of QuarkXPress this menu selection is Page > Master Guides).
- Change the values in the Master Guides fields.
Once margin guides are set when creating a new layout or project, they cannot be changed in the Layout Properties dialog. Changes to margin guides can only be made when you are editing a master page.
For an in-depth discussion of working with guides in QuarkXPress, see the QXP User Guide, pp. 37 ff.