Cannot change router name and password on C6300

> I went to www.routerlogin.net and it says I am not connected to my
> routers wifi network. [...]

   Welcome to what may be the worst error message in the world.  For an
explanation, try:

      https://community.netgear.com/t5/x/x/m-p/1365830

   Briefly, the idea is that "[www.]routerlogin.net" (or ".com") should
point to your own router, but that's true only if you use your own
router for DNS name resolution.  Regardless, you should be able to get
to the thing using its IP address, if you can determine (or guess) that.
Normally, that would be something like "192.168.0.1", but it could be
different.

> [...] I typed in my IP address into the search bar [...]

   Which "my IP address"?

   Often useful: Visit http://netgear.com/support , put in your model
number, and look for Documentation.  Get the User Manual.  Read.