Duplicate User records are generated by design to allow your supporters easy access to many of the public elements without having to create a password protected account (unless they need repeated access). The software was designed to accommodate duplicate user records - so dup records rarely interfere with its functionality and rarely need to be "managed".
Occasionally, you may need to merge duplicate user records to improve reporting (eg, donations credited to duplicate donor records) or avoid confusion (eg, an Admin places bids on their Admin user record rather than the user record with their ticket).
You can manually merge two records from the user page by selecting the two records, then clicking on Merge Users button:
Note: If both users have a ticket, you will need to return or unassign one of the tickets before merging. Also, you cannot merge business and individual user records, you will need to edit one of the user record types before merging.
Then, select the data you want to retain and Save and Merge: