I believe the only way to edit your reservation is by calling the dining reservation number. Also, assuming it is the same as it was in 2012, as long as someone shows up for the reservation, you are not on the hook for the $10 per person no show fee. So, if you think you may have 5 but are worried about the deposit if 2 of the 5 do not show, that is ok, there is no penalty since 3 did show. You can confirm by calling as well.