Once all of your ports are full, you need to expand.
Incidentally, posting this to the “Questions” section will get you a better variety of replies. In the Discussions world, we only want to discuss why your router is lacking ports, not what you can do to fix the problem.
And you can rate poster responses there too. Very hip and now!
This is very easy. Get a switch (not a router, not a hub), run a cable (you MAY need to either use a “crossover” cable or a special port on the switch) from one port of the switch to one port of the router, and you have more ports. Adding a 5-port switch to a 4-port router will give you 7 ports total (two ports are lost to the interconnection).
While this works fine, it really is a shame that, as far as I can tell, no one makes an 8-port wireless router. There really is a market for such a device.