When a customer experiences display issues such as large icons and inaccurate colors after a Windows upgrade, the most appropriate Control Panel option to address these issues is "Device Manager." The technician can use Device Manager to check and update display drivers, which are often the cause of such problems after an OS upgrade. Updating or reinstalling the correct drivers can help resolve display resolution and color issues.

A. Ease of Access focuses on accessibility features and does not directly address display driver issues.

C. Network and Sharing Center is related to network settings and does not affect display settings.

D. Programs and Features is used for managing installed programs and features but is not relevant for updating display drivers.