Visit Delta.com and sign into your Delta SkyMiles account. Click "Awards Travel."
Click on your flight and elect to "Upgrade" your seat to the next class. If any upgraded seats are available, confirm that you wish to purchase the upgrade with your SkyMiles. Your seat is now upgraded. If no upgrades are available, you will be placed in a standby list. Any available upgrades go to those in the standby list in order that you were placed on the list. Delta will automatically upgrade your seat and deduct the miles from your SkyMiles account if you are selected for an upgrade.
Call Delta to redeem your miles for an upgrade at 800-323-2323. If you don't want to upgrade online, a Delta agent will help you upgrade your seats. You will need to provide your SkyMiles PIN and flight information.
Talk to a Delta agent at the ticket counter inside the airport. Although you'll stand a better chance of snagging upgraded seats prior to your arrival at the airport, a ticket agent can place you on the standby list if no upgrades are available. You'll have to provide the ticket agent with your SkyMiles PIN and personal identification, such as a driver's license.