How to change istio log level?

I am trying to change istio log level by changing the severity from Info to warning but it does not seems to be working.

I tried changing severity in this file https://github.com/istio/istio/blob/9d92ec8dcf4472871cf587e1208b3468b62fcb47/mixer/adapter/stackdriver/operatorconfig/stackdriver.yaml

#################################################
############## Logging Config ###################
#################################################
apiVersion: “config.istio.io/v1alpha2
kind: logentry
metadata:
name: server-accesslog-stackdriver
namespace: istio-system
spec:
severity: ‘“Warning”’
timestamp: request.time