How to Impersonate local system account in c#

I am trying to start/stop a windows service in the code from a web application.The web application runs as IUSR_ComputerName, but this account does not have enough access rights to star/stop the service.

How do I impersonate the local system account, so that I can stop/start the service?

Use the impersonate tag in web.config
<identity impersonate = "true" userName = "******" password = "*****"/>