Connect the old and new hubs together using one of the four yellow ports on each box.
Make sure thd old box does not have an IP address that conflicts as described above.
Switch off the DHCP server on the old box.
Set the old box to use the same Wifi SSID and password as the new box.
Set one box to use Wifi channel 1 and the other to use channel 11, assuming that this does not conflict with your neighbours.