Hi @CarmelR . You can use a longer ethernet cable from the NBN box in the garage so you can move the new router inside the house. That will improve wifi a bit.
You can use the old router cabled to the new one to extend the wifi. On the old router, give it a new LAN address,eg. 192.168.1.2 and disable DHCP. Connect LAN to LAN. There are options for arranging the wifi.