Fixing a flat is not too hard on a moped. It is pretty similar to fixing a bike tire. I have found it easier to use the larger tire irons for dirt bikes and such. When you put the new tube in you want to be sure not to let it get pinched by the tire or it will cause a new leak and a new headache! It is more of a headache to remove the rear tire and reinstall it than the actual process of replacing the tube.
1.) Remove wheel from moped.
2.) Work one side of the tire over the rim of the wheel using a tire iron.
3.)Pull tube out.
4.) Insert new tube carefully and make sure it is seated correctly.
5.) Work tire back over the wheel rim being careful not to pinch the tube. Double check and make sure.
6.) Fill it up a little bit with air and deflate to make sure it is sitting right. I usually do this several times...fill and let it out.