From the ticket sales page, you can set/change a seat quantity per ticket type (select two Adult tickets and two Child tickets, for example).
Each ticket type displays as a separate tile. The example below shows two tickets priced at $15.00 each for the "Adult" ticket type.
Review the available ticket types, and then...
Tap or click on the number to the right of the ticket type description to select a seat quantity per ticket type.
Tap or click on ADD TICKETS TO CART to proceed to the payment screen.