Updated upgrade instructions (#1883)

* Updated upgrade instructions

* Lint

* Update index.md

content/docs/setup/kubernetes/upgrading-istio/index.md

@@ -15,23 +15,32 @@ In the following steps, we assume that the Istio components are installed and up
 ## Control plane upgrade
 
 The Istio control plane components include: Citadel, Ingress gateway, Egress gateway, Pilot, Policy, Telemetry and
-Sidecar injector. We can use Kubernetes’ rolling update mechanism to upgrade the
-control plane components.
+Sidecar injector.
+
+### Helm upgrade
+
+If you installed Istio with [Helm](/docs/setup/kubernetes/helm-install/#option-2-install-with-helm-and-tiller-via-helm-install) the preferred upgrade option is to let Helm take care of the upgrade:
+
+{{< text bash >}}
+$ helm upgrade istio install/kubernetes/helm/istio --namespace istio-system
+{{< /text >}}
+
+### Kubernetes rolling update
+
+You can also use Kubernetes’ rolling update mechanism to upgrade the control plane components. This is suitable for cases when Istio hasn't been installed using Helm.
 
 First, generate the desired Istio control plane yaml file, e.g.
 
 {{< text bash >}}
-$ helm template --namespace istio-system --set global.proxy.image=proxy \
-  --values install/kubernetes/helm/istio/values-istio.yaml \
-  install/kubernetes/helm/istio >> install/kubernetes/istio.yaml
+$ helm template install/kubernetes/helm/istio --name istio \
+    --namespace istio-system > install/kubernetes/istio.yaml
 {{< /text >}}
 
 or
 
 {{< text bash >}}
-$ helm template --namespace istio-system --set global.proxy.image=proxy \
-  --values install/kubernetes/helm/istio/values-istio-demo-auth.yaml \
-  install/kubernetes/helm/istio >> install/kubernetes/istio-demo-auth.yaml
+$ helm template install/kubernetes/helm/istio --name istio \
+    --namespace istio-system --set global.mtls.enabled=true > install/kubernetes/istio-auth.yaml
 {{< /text >}}
 
 If using Kubernetes versions prior to 1.9, you should add `--set sidecarInjectorWebhook.enabled=false`.
@@ -45,7 +54,7 @@ $ kubectl apply -f install/kubernetes/istio.yaml
 or
 
 {{< text bash >}}
-$ kubectl apply -f install/kubernetes/istio-demo-auth.yaml
+$ kubectl apply -f install/kubernetes/istio-auth.yaml
 {{< /text >}}
 
 The rolling update process will upgrade all deployments and configmaps to the new version. After this process finishes,