If you want to cleanse your data by checking for duplicate records you can begin by using the Merge Stakeholder function under Data Maintenance in Admin.
Here I have requested possible duplicates for stakeholders who have a surname starting with P through T.
I receive a list of possible duplicates. I decide that sue sharp (26229) and Sue Sharp (26302) are the same person so I click "merge from" (red highlighted box) and click "merge to" (green highlighted box). And then click the "Merge" button at the bottom of the list.
All the contact and interaction information from sue sharp (26229) is transferred over to Sue Sharp (26302) and STK26229 is deleted. Contact details are not duplicated and no data is lost.
Merging can never be an automatic process. It takes a user who knows their data to decide whether records are duplicated.