Peace Be Upon You,
Changing an existing SharePoint Web app from classic authentication mode to claims based authentication mode can’t be done from central administration, but it can be done using power shell.
Here is a simple PowerShell script which changes the web app’s authentication mode to claims based:
$webApp = Get-SPWebApplication “http://webapplicationname:port”
#webApp.UseClaimsAuthentication = “True”;
Once you have executed the above PowerShell script, if you go to your web app’s authentication provider settings, you should see:
All thanks to power shell 🙂