You can adjust the number of travelers from either the Skiplagged home page or at the top of the search results. You will find the option to change the number of adults and children traveling. Click on the drop-down traveler menu to change the number of travelers. As you adjust the number of travelers, the price will adjust once you click on the blue Search Flights button.
Selecting travelers has to be done before you get to the final checkout page. If you want to change the number of travelers, you will need to go back to the search results page and make changes there, select the flight and then continue to the final checkout page.
*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.