$users = Get-ADUser -SearchBase "OU=Users,OU=123,OU=ch,OU=lda,DC=domain,DC=jalol,DC=com" -Filter * -Properties * | Where {$_.Enabled -eq $True} | Select Surname,GivenName,SAMAccountName

$Users = Get-ADUser -SearchBase "OU=Users,OU=123,OU=ch,OU=lda,DC=domain,DC=jalol,DC=com" -Filter * -Properties * | Where {$_.Enabled -eq $True} | Select Surname,GivenName,SAMAccountName,DistinguishedName

ForEach ($User In $Users)
{
$DN = $User.DistinguishedName
$GivenName = $User.GivenName
$Surname = $User.Surname
$Display = $User.DisplayName
$NewName = "$Surname, $GivenName"
If ($Display -ne $NewName) {Set-ADUser -Identity $DN -DisplayName $NewName}
}