Changing the wireless channel on the router or access point is the most appropriate first step to resolving fluctuations in signal strength due to potential interference from other wireless devices. This type of interference can cause the received signal strength to vary, leading to intermittent connectivity for the client device.

• Updating the laptop's operating system, while potentially helpful for other issues, is not directly tied to improving wireless signal strength consistency.
• Recommending high-gain antennas may help increase wireless signal strength overall but may not address interference problems that cause intermittent connectivity.
• Removing physical obstacles, though potentially beneficial, is moot here because the issue persists even when the laptop's location is unchanged, implying that barriers are not responsible for the fluctuating signal strength.