The wheels rust to the axles and are difficult to remove. Remove the pin and hair clip on the side you want to remove. Spray Liquid Wrench or some other rust buster liberally on the wheel hub and the axle.
Put the transmission into forward till position. Prop up the side of the tiller you are working on. Secure a large (24-36") pipe wrench onto the hub of the wheel you want to remove and turn it. You might have to jump up and down on the wrench or use a cheater bar. Once you break the wheel loose, it will turn counter clock wise and back off the axle.
To remove the other wheel, you will need to put the wheel you removed back on. Put a pipe wrench on the hub of the wheel you removed and let it run into the ground. Prop up the other side and do the same thing you did on the first wheel. The pipe wrench will keep the wheel from turning through the transmission.