Before you autoroute, set your design rules (DRC) parameters. Open up the DRC and in the Sizes tab, set the "Minimum Drill" text box to the desired hole diameter for vias. You can also do this with net classes but the DRC method is easier for most people.
If you've already routed and want to change sizes (not a good idea since it will probably make vias bigger and cause clearance violations) you can turn off all layers except vias:
display none vias
Then group them all, and select Change-->Drill, then type in your desired drill diameter. Make sure to run a DRC afterwards to check for clearance violations.
The Aussie Shield
: breakout all 28 pins to quick-connect terminals