Each airline has it's own rules when it comes to seat assignments.
When possible, we will assign seats when complimentary seat assignment options are offered and available. Rules vary by airline as some may or may not allow seat assignments prior to check-in. Some airlines will allow you to check in online 24 hours to the flight. You can do this on the airline website using the PNR number associated with your flight. (This is the 6 characters located next to your flight information in your documentation.). Some airlines will charge fees for advance seating so it is best to check with the individual carrier as their policies are ever-changing.
Should you wish to obtain seating with additional legroom most airlines charge a fee to upgrade to premium seats. You will need to contact your airline directly to obtain these seats.