Delta ( rewards its frequent flyers with free and unlimited first-class upgrades. Sign up for a rewards membership, travel as you normally would and you will eventually earn enough miles to achieve silver medallion status, which starts the free upgrades. Upgrades are subject to seat availability. Keep wracking up miles to achieve progressively higher upgrade priority as a gold, platinum or diamond medallion status member.

Step 1.

Go to Delta's website to sign up for a free Skymiles account. Go to the "Skymiles" tab in the upper right corner, scroll down and click "Join Skymiles." Fill out the electronic application.

Step 2.

Travel on Delta or one of 16 affiliated airlines, such as Alaska Air, to collect medallion qualification miles, or MQMs. Provide your Skymiles number when booking flights, or sign into your Skymiles account and book online through Delta. MQMs are calculated by fare type and flight length.

Step 3.

Achieve silver medallion status at 25,000 MQMs. Silver medallion status gives free upgrades, but higher status members enjoy more benefits. Gold status is at 50,000 MQMs, platinum at 75,000 and 125,000 gets you diamond status.

Step 4.

Make a reservation with Delta and provide your medallion status Skymiles number. Delta will automatically upgrade your ticket to first class for free if a seat is available. Silver, gold, platinum and diamond medallion members are given progressively higher seating priority.