When upgrading a GKE cluster, all you need to do is issue a scaling command that modifies the number of instances in your minion group. You can resize the node pools that control your cluster with the following:

gcloud container clusters resize [CLUSTER_NAME] 
 --node-pool [POOL_NAME]
 --size [SIZE]

Keep in mind that new nodes are created with the same configuration as the current machines in your node pool. When additional pods are scheduled, they'll be scheduled on the new nodes. Existing pods will not be relocated or rebalanced to the new nodes.

Scaling up the AKS cluster engine is a similar exercise, where you'll need to specify the --resource-group node count to your required number of nodes:

az aks scale --name myAKSCluster --resource-group gsw-k8s-group --node-count 1