I got the same question and they did send me an email, here it is:
We have heard that Coach Leather Cleaner works well. We actually havent experimented at all with cleaning the leather, as we like a worn-in look. But people have said that the Coach cleaner works well. Any light cleaner ought to work, or a gentle brushing with a suede brush. You could consult a local shoe-repair store which will have many options for leather cleaners.