How do I keep a running total of my tickets reservations?

On a registration form, I've given a choice of reserving 1-10 tickets but have a limited amount of tickets so I need to keep a running total. 

Based on the description you kindly provided, the best fit would be using the Quantity Gift Registry widget with your item: https://widgets.jotform.com/widget/quantity_gift_registry

I hope this helps. If you need further assistance please let us know. Thank you.