How can I change security password on a Nighthawk R7000 Router I purchased used

> Model: A7000|Nighthawk AC1900 WiFi USB Adapter - USB 3.0

   Nothing to do with anything?

> How can I change security password on a Nighthawk R7000 Router I
> purchased used

   Which password is "security password"?  Which password is _not_ a
"security password"?

   You might try this radical concept which works for some people:

      https://en.wikipedia.org/wiki/RTFM

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual (at least).  Read.
Look for "Types of Logins" and "Reset".  And "Specify Basic WiFi
Settings".  Further reading might not hurt, either.

The first thing to do with any second hand device is to reset it. The removes old passwords and, more important, any settings that the previous user had configured to get it to work on their network.

How do I perform a factory reset on my NETGEAR router? | Answer | NETGEAR Support

Then treat it as a brand new devuce that has just come out of its box.

Manuals are always a good place to start.

Visit the support pages:

Support | NETGEAR

Feed in your model number and check the documentation for your hardware.

That page will also have any software, firmware and drivers for your device, if they exist.

Look for the model number on the label on the device.

Begin with the Quick Start/Installation Guide.

There may also be some helpful videos on what to do.

You may have done that already. I can't tell from your message.

I mention it because Netgear gave up on supplying paper manuals and CD versions some years ago and people sometimes miss the downloads.

Is the Model: A7000|Nighthawk AC1900 WiFi USB Adapter - USB 3.0 listed in your footer involved in this in anyway? Or did you just click the first thing that popped up when you wrote your message?