Kubernetes Certificate renewal V1.12

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###Certificate renewal process of V1.12 and does it require any downtime ?

Cluster information: 3 Master and multiple worker

kubernetes-cni-0.6.0-0.x86_64
kubeadm-1.12.0-0.x86_64
kubectl-1.12.0-0.x86_64
kubelet-1.12.0-0.x86_64

docker-ce-18.06.0.ce-3.el7.x86_64

Can some one help with step by step process of renewing certificates in V1.12

Kubernetes version:V1.2
Cloud being used: BARE-METAL
Installation method:kubeadm/kubectl
Host OS: redhat 7
CNI and version: 0.6.0-0.x86_64
CRI and version:

Please let me know if any details required .