Dear Melanie,

If two contact cards were created for the same contact by mistake and only one is required, the usual process is to:
1) manually fill all the relevant fields in one of those cards, so that one card would contain all the information in the contact card;
2) use System module -> Settings -> Conversions - Contacts and Conversions - Master to merge the not required contact with the required one for proper history purpose.
This will required database export and import procedure though, so most often just one of both contacts is closed...

Best regards,
Eberstein Business Solutions