How can I replace my AirPort Extreme (2016)?

Not much to go on with your post, so it would be difficult to offer advice on, whether or not, you should replace this Apple base station.

As already mentioned by the others, if it is no longer working, then a replacement would be in order ... and should that be the case, without knowing your networking requirements, what you should replace it with will be just guesswork on our part.

The more you can provide us, the better any of us can try to assist you.

Ref: Writing an effective Apple Support Communities question

Assuming that the AirPort Extreme is still working......it likely is.....is there a special feature or option that you need from a wireless router that the AirPort Extreme does not offer?

The question is probably closer to whether you want to replace the Extreme on your schedule, or on its schedule.

Does it still work? If so, you can continue to us it. If it doesn't work, you'll need to get something else.