Unable to update my R8500

You gave us nothing to go off.
To get a hold of support. Click on "MyNetgear" at the top.
Register an account (or login) and then the device.
From there you can start the support process. Keep in mind that its only free for the first 90 days.
There's a support site with access to manuals, firmware, install guides, etc.
Go to https://www.netgear.com/support/
Type in your model number and from there it'll take you to the above.
Its a great resource to start with.

https://kb.netgear.com/23960/How-do-I-manually-update-the-firmware-on-my-NETGEAR-router