I have already registered 5 PCs. Can I register more?
You can only register up to 5 PCs per Kakao Account. If you want to add another PC, you must deregister one of your current PCs.
[How to deregister on mobile]
Go to More > Settings > Privacy > Manage Devices.
[How to deregister on PC]
Log in to the PC that you want to deregister and go to Settings > General > Deregister Desktop.