Having duplicate contact records can be very confusing and lead to problems with data integrity. However, you need to be careful when deleting a duplicate contact record to ensure that you're not losing any of the associated information. For example, if a communication record is tied to "Jane Smith", but it should be tied to another "Jane Smith" record, you need to find which records are associated with the wrong Jane Smith and update them to be associated with the correct record.
Note that Contact records tied to user accounts cannot be deleted.
Step 1: Rename the incorrect entry to highlight it
From the contact record, change the display name so that it is easily find-able when looking at a record, for example, change the display name "Jane Smith" to "Jane Smith REPLACE"
Step 2: Scan all possible records for the incorrect entry
Scan the records which could contain the incorrect entry for the new flagged record ("Jane Smith REPLACE"). When you find them, replace the incorrect entry with the correct one.
Step 3: Delete the incorrect entry
Once you're satisfied you've associated all relevant records with the correct entry, you can safely delete the duplicate contact record by using views or the active contacts list.