better to use a switch not a

router. connect the switch (nowadays, don't even need to distinguish uplink and downlink port) to the router as you connect your computer now. connect all computers to the switch. You done! don't have to do anything. If you use a router, you have to disable the DHCP service, in other words, you just use the router as a switch.
Another way is to use a wireless access point. connect it to the router.