To uninstall KernelCare do the the following:
For CloudLinux, CentOS, RHEL, Virtuozzo, OpenVZ:
$ yum remove kernelcare
For Ubuntu, Debian, Proxmox VE:
apt-get remove kernelcare
dpkg --remove kernelcare
This will also unlink the system from its activation key (provided there is network connectivity to the CLN Portal). However, you'll need to remove the license from the CLN Portal manually if you don't plan to use the service anymore.