When changing a Southwest flight, the plus and minus signs displayed next to the prices on the "Select New Flights" page indicate whether the new flight costs more or less than the original itinerary. A plus sign (+) indicates that the new flight is priced higher than the original one by a certain amount, which will be charged to your account. In contrast, a minus sign (-) indicates that the new flight is priced lower than the original one by a certain amount, which will be refunded to you via the original form of payment or as a flight credit. If the price for the new flight is $0, it costs the same as your original booking, allowing you to switch without incurring additional charges or receiving a refund or flight credit.