iPhone trade-in

I recently purchased an iPhone 12 and chose to pay it monthly. I received it a few days ago and realized that I could've gotten the iPhone 13 instead considering the price difference wasn't that big and the 13 is still better than the 12. Would it be possible to trade-in my monthly paid phone for a new one and just pay the difference in taxes and monthly payments? I haven't made my first payment yet so technically the first payment would be towards the 13 making no difference in the price.