PowerShell to update content type in SharePoint

function LoadSharePointSnapin
{
  $snapin = "Microsoft.SharePoint.PowerShell"

  if ((get-pssnapin $snapin -ea "silentlycontinue") -eq $null)
  {
    Write-Host -ForeGround Green "Loading SharePoint Snap-In $snapin."
    Add-PSSnapin $snapin
  }
}

try
{
  write-host -ForeGround Green "** Start Updating Content Type **"
  LoadSharePointSnapin
  Start-SPAssignment -Global

  $spSiteUrl = read-host "Enter Your Site Collection Url  "
  $spSite =  Get-SPSite -Identity $spSiteUrl
  $rootWeb = $spSite.RootWeb

  $MyListContentTypes = $rootWeb.ContentTypes                                                         
  if ($MyListContentTypes -ne $null)
    {
         $ct = $rootWeb.ContentTypes["Content Type Name"]                                     
         if($ct)                                                           
         {
             $ct.FieldLinks[$ct.Fields["Field1"].Id].Required = $False
      $ct.FieldLinks[$ct.Fields["Field2"].Id].Required = $False
      $ct.FieldLinks[$ct.Fields["Field3"].Id].Required = $False
             $ct.Update($true)
         }     
    }     
  write-host -ForeGround Green "** End **"
  Stop-SPAssignment -Global
}
catch
{
  Write-Host ""

  If ($_.FullyQualifiedErrorId -ne $null)
  {
    Write-Error $_.Exception.Message
  }
}