How to remove a device from my Wifi Network

Here is the solution from xfinity website.
https://www.xfinity.com/support/articles/manage-wifi-devices-my-account
How to Manage and Remove Registered Xfinity WiFi Devices

If you are an eligible Xfinity Internet subscriber, you have access to Xfinity WiFi hotspots nationwide so you can stay connected on-the-go at no additional charge. You can register up to 10 devices on your account to access Xfinity WiFi hotspots.

How to Remove or Rename Registered Devices

To remove or rename a device registered to access Xfinity WiFi hotspots:
    Sign in to My Account or the My Account app and click or tap the Services tab/icon.
    From the Services page, under Internet, click Manage Internet.
    Scroll down to Xfinity WiFi Hotspot Connected Devices and click Manage Devices.
    Click Rename to edit your device name.
    Click Remove to remove your device from the list of registered devices. A confirmation message will appear.
    Note: If you've reached your limit of 10 registered devices, you must remove a device before you can add another.

Note that the device list at xfinity site shows the mac address of your laptop.
To get the mac address,  go to "search" on the bottom left of the window screen and enter "cmd"
At the command prompt,  enter "ipconfig /all" and you will then see "pysical address" which is the same as the mac address (media access control address).
The physical address is the one under "wireless LAN adapter local area connection*1" in my case.

5 month old dead thread now being closed...