Perform a Factory Default Reset on the old AirPort Extreme (AEBS)
Power down the AEBS by pulling the power plug from the back of the device
Hold in the reset button and keep holding it in for 8-10 seconds while you plug the power back in
Release the reset button and allow 40-45 seconds for the AEBS to restart to a slow blinking amber light
Connect an Ethernet cable from one of the LAN <-> ports on the new AEBS to the WAN port (circle of dots icon) on the old AEBS
Open AirPort Utility - Select the old AEBS - Click Manual Setup
Click the Base Station tab located below the row of icons to assign a device name to the AEBS, device password, adjust Time Zone settings, etc.
Click the Wireless tab
Wireles Mode = Create a wireless network
Wireless Network Name = Your choice
Radio Mode = 802.11b/g compatible
Channel = Automatic
Wireless Security = Recommend WPA2 Personal or WPA/WPA2 Personal
Wireless Password = Your choice
Confirm Password
Click the Internet icon
Click the Internet Connection tab below the icon
Connect Using = Ethernet
Connection Sharing = Off (Bridge Mode)
Update to save settings and allow 40-45 seconds for the AEBS to display a green light
Very important.....power off the entire network....all devices.....order is not important
Start the modem first and let it run by itself for a moment or two
Start the new AEBS the same way
Start the old AEBS the same way
Continue starting devices one at a time about a minute apart until everything is powered back up
Check the network for proper operation.