Model R6400v2, looking how to change the router name and it's password

One way forward is to use the Reset button on the router to load the Factory Default Settings, after which all of the info you need is printed on the bottom of the router.

Details: On the Netgear R6400v2 router there is a Reset button on the back of the router, next to LAN port 4. The Reset button is set back inside of a hole to prevent accidental pressing, so one must use a paper clip or similar implement to press it. With the router powered on, press and hold the Reset button for 5-10 seconds until the power light on the front of the router turns orange, then then release the Reset button. Allow 3-4 minutes for the router to cycle, then use the Wi-Fi Network Name + Key printed on the bottom of the router to join a laptop or other device to the router's wireless network. Then use the website + username + password underneath "Router Login" printed on the bottom of the router to administer the router.
When administering the router, the Wi-Fi Network Name + Key can be changed on the Basic tab, under Wireless.
When administering the router, the password to administer the router can be changed on the Advanced tab, under Administration -> Set Password.