If it transpires that a single contact is represented by two or more records in the Contacts database the records should be merged to consolidate all details into a single record. This prevents inconsistencies and confusion when viewing or changing their details. A typical problem is modifying an address in one of the records but then inadvertently using the other record to address a letter to them.
To consolidate the contact records into a single record, including all Transactions and Requests associated with them use the Merge (or Merge Recs) command on the Contacts or Requests screen.