I've installed Grafana using helm as follows:

helm install --name grafana stable/grafana

Now I want to update the previous installation without deleting it to set an env variable as follows:

helm install --name grafana stable/grafana --set env.GF_AUTH_ANONYMOUS_ENABLED=true

but I've got an error

Error: a release named grafana already exists

If I delete the previous installation I will probably delete the dashboards I've already made