Thank you for your question HoldenComeau!
You can create a cname or A record in the Simple DNS Zone editor. If you are on a VPS or Dedicated server, you can use the Advanced DNS Zone editor.
Shared servers no not have access to cnames like ftp, mail, cpanel, webmail, and so forth. To have a cname changed on a shared server, you will need to have support add them in the backend. Please see the following link for more information.
How do I make custom DNS records?
Best Regards,
James R