So I recently discovered a loophole when flying Delta a few weeks ago and exploited the hell out of it.

The end result? Not only did I get a more desirable schedule, I was upgraded to First class on all 3 of my flights.

How to Get It / What I Did:

1. Wait for a change/delay in your flight schedule. This part is really just getting lucky. When Delta has a delay in excess of 15 mins (I know there is a threshold), a warning message pops up on its website/iPhone/Android app informing you of the change and asking you if you’d like to find alternate flights.
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2. Select “View Alternates.” You should notice that it shows very clearly that the options include first class. At least they did for me (Note: I’m a Silver Medallion with Delta– pretty low on the totem pole, but some status none-the-less).
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3. Select your alternate if acceptable with you. In my case, I got an error message to try again or call. If you get the same error, continue to step 4: 
4. Write down your alternate flights and call Delta. Being tight on time, I called Delta and explained the situation, they checked and agreed that the delay (even though just 15 mins) would make my connection difficult. I gave them my desired flights–make sure to write these down before calling–and she got right to work. It took about 10 mins on hold, but she confirmed my new flights. I reminded her that the website said/ implied that an upgrade was part of the deal and was told, “We can’t just upgrade you to First, but your Medallion status has been noted and you’ll be added to the standby upgrade list.” So, essentially, once ticketed, I would be cleared immediately for an upgrade so long as there are seats. Fair enough.
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5. Go to a gate agent. Getting off the phone I saw the new confirmation email come through and was pleased to see that at least 1 of 3 flights had an assigned seat in First. I walked over to the gate agent and explained that my flights had changed due to delays/cancellations and that I was told my new flights would be upgraded to First, but only 1 of 3 had been changed, implying the phone rep must have made a mistake. He checked on the flight and was able to, reluctantly, confirm a seat on the 2nd of 3 flights assuring me that I was high on the upgrade list now for the 3rd leg.
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6. Wait. Sure enough, right as boarding began, my name was called for an upgrade.

Success! All 3 flights switched to First all for a few minutes on the phone and a few minutes haggling with gate agents.

BOTTOM LINE: Your mileage may vary, but its very likely you can get upgraded to First by taking advantage of flight delays.