Before upgrading a cluster, make sure you read the release notes carefully.

The upgrade procedure on control plane nodes should be executed one node at a time. But in the upgrade, it's better to upgrade the control plane first and then worker nodes one by one.

Upgrade Control nodes:

Find the latest patch release for Kubernetes 1.26.2 using the OS package manager

sudo apt update
sudo apt-cache madison kubeadm
# find the latest 1.26.2 version in the list
# it should look like 1.26.2-00

• Upgrade kubeadm

sudo apt-mark unhold kubeadm && \
sudo apt-get update && \
sudo apt-get install -y kubeadm=1.26.2-00 && \
sudo apt-mark hold kubeadm

• Verify that the download works and has the expected version

kubeadm version

• Verify the upgrade plan

kubeadm upgrade plan

• Choose a version to upgrade to, and run the appropriate command

sudo kubeadm upgrade apply v1.26.2

• Once the command finishes you should see

[upgrade/successful] SUCCESS! Your cluster was upgraded to "v1.26.2". Enjoy!

[upgrade/kubelet] Now that your control plane is upgraded, please proceed with upgrading your kubelets if you haven't already done so.

• Prepare the node for maintenance by marking it un-schedulable and evicting the workloads

# replace <node-to-drain> with the name of your node you are draining
kubectl drain <node-to-drain> --ignore-daemonsets

• Upgrade the kubelet and kubectl

sudo apt-mark unhold kubelet kubectl && \
sudo apt-get update && \
sudo apt-get install -y kubelet=1.26.2-00 kubectl=1.26.2-00 && \
sudo apt-mark hold kubelet kubectl

• Restart the kubelet

sudo systemctl daemon-reload 
sudo systemctl restart kubelet

• Bring the node back online by marking it schedulable

# replace <node-to-uncordon> with the name of your node
kubectl uncordon <node-to-uncordon>

• Verify the status of the cluster

kubectl get nodes

Upgrade worker nodes

• Upgrade kubeadm

# runs in worker nodes
sudo apt-mark unhold kubeadm && \
sudo apt-get update && \
sudo apt-get install -y kubeadm=1.26.2-00 && \
sudo apt-mark hold kubeadm

• For worker nodes this upgrades the local kubelet configuration

# This would run in control node 
sudo kubeadm upgrade node

• Prepare the node for maintenance by marking it un-schedulable and evicting the workloads

# replace <node-to-drain> with the name of your node you are draining
kubectl drain <node-to-drain> --ignore-daemonsets

• Upgrade the kubelet and kubectl

# runs in worker nodes
sudo apt-mark unhold kubelet kubectl && \
sudo apt-get update && \
sudo apt-get install -y kubelet=1.26.2-00 kubectl=1.26.2-00 && \
sudo apt-mark hold kubelet kubectl

• Restart the kubelet

sudo systemctl daemon-reload 
sudo systemctl restart kubelet

• Bring the node back online by marking it schedulable

# replace <node-to-uncordon> with the name of your node
kubectl uncordon <node-to-uncordon>

• Verify the status of the cluster

kubectl get nodes

Reference

Upgrading kubeadm clusters - kubernetes.io