Worker nodes can be managed via the web dashboard as described here. Once you have installed kubectl, you can also manage them via the command line interface (CLI) in order to automate creation, deletion and upgrades of nodes.
To get a list of all nodes execute:
kubectl get nodes -o wide
Every node is managed by a machine resource in the kube-system namespace, which are bundled into machineDeployments (for more information see documentation). To list all machineDeployment resources, execute:
kubectl get machineDeployments --namespace kube-system
If you want to change a machineDeployment, you can edit the machineDeployment resource directly:
kubectl edit machineDeployment ${machineDeployment} --namespace kube-system
When a machineDeployment is edited, the machineController will take care of updating the respective machines. Further explanation to the existing fields and update strategies can be found in the Cluster API documentation.