During your GFNY race registration, you select your preferred jersey size. You can change your jersey size selection in your gfny.cc account any time until 21 days before the race. After the online changes timeframe is closed, you can go to the expo and visit the Jersey Exchange booth. Because only a limited number of exchange jerseys are available, your preferred jersey size may not be immediately available. Check back regularly because size exchanges happen continuously throughout the day and your preferred size can become available.