Forms Based Authentication on an exisiting SharePoint 2010 Classic Mode web app

If you are trying to implement Forms Based Authentication on an exisiting SharePoint 2010 web application there is no way through Central Administration to change your existing Classic Mode Web Application to Claims Based.  Below is a quick and easy PowerShell script that will accomplish this for you.

$webapp = Get-SPWebApplication "http://yourwebappurl/"
$webapp.UseClaimsAuthentication = "True"
$webapp.Update()
$webapp.ProvisionGlobally()

At this point you are now set to complete the steps to implement Forms Based Authentication on your Web Application.