When you select the itinerary that you want, the details of your booking will appear with a total price quoted. Below that price, you will find the option to change the number of adults and children traveling. Click on the dropdown menus ("1 Adult" and "No Children") to change the number of travelers. As you adjust the number of travelers, the price will adjust.*
*Note: The price adjusts by multiplying the fare for a single ticket by the number of tickets you've selected. Please note that the airline may not have that number of seats available at the lowest price, so the total you see when you finalize your booking may ultimately be higher.