Go5G Next - Phone Upgrade

Hello,

So I just switched my plan to Go5G Next, and was wondering how the phone upgrade works. I am still paying on my current device from my previous plan, but when I click on upgrade device, it allows me to make an upgrade. With that said, If I upgrade, will I still owe the amount on my current device as well? I am a bit confused and would appreciate any assistance.

Thank you!