Answered question
Just click to apply the upgrade first then click on the current one and choose swap!
The answer’s here for those concerned about loosing the upgrade if they remove it : https://community.fizz.ca/questions/1845941-anyone-able-switch-upgrades-yet#answer_4219466
Other answers
What happens to the upgrade that you remove though? Is it lost or does it return to your upgrade list? That's my concern with trying to swap out upgrades.
I spammed the swap button and nothing seemed to happen. So I removed the upgrade instead. Now got to wait two next billing cycle for my new upgrade to take effect! #sadpotato
Nice! Hopefully you don't lose the upgrade you swapped out.