1. In your account, go to My Domains > Manage my domains
2. Select the domain to configure
3. Click on Edit DNS Zone
4. Add/edit the DNS records
5. Save settings
The new records will take effect within 24 hours.
Note: this option is only available if the name servers of the domain are EuroDNS' ones (ns1.eurodns.com / ns2.eurodns.com)