If you find a customer has duplicate accounts, you can and should merge them into one and control which data takes precedence between the two versions. 

Merging is preferable to simply deleting the duplicate account because they will both contain essential customer information for the same Client.

Search for both Client accounts, and select them both. From the Action Menu, select Merge Duplicate Contacts, and proceed to merge the up-to-date field(s) into the out-of-date field(s).

To confirm your choices, scroll to the bottom of the page and click 'Merge & View Contact'