Limit submissions on select

I’m selling a limited number of places on a camp on my website so I set the limit to 6 on the select that I’m using for choosing which week parents are booking their kids into.

As happens, somebody’s booked into the wrong week, but what do I do with limits on the form options? I don’t want to allow too many people to book onto one option or remove the option if there’s still actually one available.

Do I update option A to 5 and option B to 7 to account for the switched place or does that reset the totals to the limit from when I update the form?