From your dashboard, click on the 'Events' tab.
Select the event that you would like to change the ticket quantities.
Select 'Edit event and tickets' from the left-hand menu.
Under 'Create tickets' select the ticket you would like to change the quantity for, or click 'Add a new ticket type' if you would like to create a new ticket type.
The 'Quantity' field is the limit of the number of tickets it will allow to be sold, excluding any that have been sold.
If you would like to set a maximum quantity across a number of ticket types then click here to learn about how to do this.