A few ways really...
1. Get an XTension like XpertScale.
2. Save page as an eps with bleed etc, and enter 98% in the save dialog box.
3. Select All, Group, then use the item select tool to grab a corner and scale. It's only a last resort method, though, as not everything scales evenly (eg., tabs, indents, baseline grid...). Still, it has it's uses.
4. If you are only printing at 98%, then use the scaling feature built into the print dialog box.