Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Model # XXXXX
Serial # XXXXX
There's a couple of options.
First, the hubcap can be pried off gently working your way evenly around the outside. Underneath is a cap lock screw, bell washer, and flat washer holding the wheel to the axle. There's locktite on the screw, so you'll need a bit of pressure on the wrench to break it free. Most tire repair shops will patch these types of tires as well depending on how big and where the hole is. If it's too big you can replace it or add a tube.
Second, if the hole is a 1/4 or less and in the tread area, you can go get a bottle of tire sealant (Briggs, Slime, Pneumaseal, not the canned stuff sold for car flats) and put this in the tire. The advantage is that you don't have to remove the tire and it helps prevent flats in the future. Putting some all the way around the four tires is a great bit of headache insurance.
Hope this helps!