Sometimes airlines can make schedule changes between the time of booking and the time of departure.

It is always recommended to re-confirm your flight at least 24 hours prior to travel. 

You can view all of your flight information directly on the airline website - you will need to enter your airline booking number (PNR) in the booking reference field and your last name.  You can find your PNR in the flight information portion of your portal. in some cases your flight may indicate a specific airline and then say "operated by" another airline (Ex: a Delta Airlines flight operated by Air France). This is because airlines have agreements called "Codeshares" for specific routes. It allows them to sell a ticket on that route and have the passenger travel with a partner airline. 

Once you access your flight details, you can also add your contact information to receive change alerts. 

Lastly, when an airline actions a schedule change we will update your flight details in your Traveler Portal Account which will trigger a 'change alert' e-mail to you.  However, remember that airlines can action last minute changes so it is always wise to check in 24 hours prior and to monitor your flight status.