When a device is slow to respond, checking for and increasing available system resources, such as RAM and CPU, can significantly improve performance. In this scenario, where the hardware has been verified to meet the requirements and the issue began after a system upgrade, it's possible that the upgrade might be utilizing resources more heavily, leading to the sluggishness. Therefore, the technician should check and potentially increase the available resources. Reinstalling the operating system would be much more disruptive and is not the best first step without trying less drastic measures first. Disabling the antivirus would be a security risk and might not resolve the performance issue. Performing a system file check, while useful for corrupted or missing system files, is less likely to address performance issues related to system upgrades.