You can use either a http connection or an https one. By default if you just type in the router's IP, it will simply use the unencrypted connection, but you can force a secured one, though your browser will warn you about the self signed certificate.
Often if you are on your local home network, it is unlikely for someone to be trying to capture that traffic.
If they have that level of access, then your network and devices are likely already deeply compromised.
It was more of pointing out why it is not as much of a concern to not use HTTPS over the LAN to the router on a home network.
If you are not sharing your network with someone you do not trust, then it is not too much of a concern since for the unencrypted connection to be expired, an attacker will need to already be on your LAN, e.g., physically connected to the router, or at least connected to the WiFi and then attempt to do an ARP poison attack in an attempt to capture the traffic related to the unencrypted login.
Assuming you have a decently strong WiFi password, cracking it will be extremely difficult, especially since even with WPA2, you cannot really have a set of precomputed hashes to speed up the process.
If one of your computers is compromised to allow for remote access, then the attacker already has a level of access that would make HTTPS meaningless at least for that system, since they will have essentially have access to info before it is ever encrypted.
It is unlikely that any of this has happened with your network, thus unless you are sharing your network with a bunch of people who you do not want accessing the router's web UI, and you suspect they will attempt to intercept traffic on the network in an attempt to gather the admin login, then there is not much of a need to go out of your way to use the HTTPS page.
