upgrade my iPhone 11 to iPhone 13 pro

A few items for your checklist:

1. Purchase iPhone 13 Pro here.
2. Apple Trade-in here.

You need to enter your product serial number and answer some simple questions to receive a price quote. 😉

Note: You can trade-in your previous iPhone after you have completed the upgrade, no rush.

Go to the Apple website. https://www.apple.com/

Then at the top left, click the 3 lines. From there, select iphone. Then find iPhone 13 pro. Then at the top right, press buy. The process can vary a little depending on your device. I have an iPad mini 5th gen. There will be an option to trade in your old iPhone if you so desire.

You can also buy it from Amazon, Best Buy, Ebay, your choice of phone carrier (like Verizon, t mobile, etc) and many other places.