Hi,
You have to delete the cname first and then recreate it.
$zone = "mydomain.com"
$name = "myhost"
$cname ="mycname"
$DNSServer = "mydnsserver.mydomain.com"
Remove-DnsServerResourceRecord -Name $name -ZoneName $zone -RRType CName -ComputerName $DNSServer -Force
Add-DnsServerResourceRecordCName -Name $name -ZoneName $zone -HostNameAlias $cname -ComputerName $DNSServer
You would need permissions to create the record as well. Once you've created its, you're the owner of it and can delete its again.