Upgrade SmartWatch

Has anyone ever tried to upgrad a SmartWatch? I currently have a Galaxy SmartWatch, but I switched to an Iphone 15 a few months back. I'd like to upgrade it to an Apple Watch, but I can't figure out how to do it. I click on upgrade, it takes me to a new screen to find the device, I add the device to my cart but there is no upgrade option anywhere. It's just wanting me to buy it outright or do a monthly plan separately. I don't want this Galaxy watch anymore because it's absolutely useless with an iPhone.