The first thing you must do is uninstalling KMSpico.
After that, activate with the new license. Settings > Settings > Activation
Sometimes, some extra steps are needed, based on the kind of license you buy, but in this case, you are given instructions from the seller.
As you understand, you don't need to go for a clean install of the system. But you will need a system cleaning after.
Let me know when you are ready. I'll be here.