Final answer:
In adherence to security best practices, the 'Administrator' account should be renamed to reduce the risk of unauthorized access.
Step-by-step explanation:
According to security best practices, the user account that should be renamed is D. Administrator. This is because default account names such as 'Administrator' are well known to attackers and can be easily targeted. By renaming the Administrator account to something less predictable, you reduce the risk of unauthorized access. The other account names, while perhaps could be more descriptive, do not pose the same level of security risk as a default administration account name.