A lot of this depends on what IP addresses are being used by the wired and wireless networks. If the wireless router is using dhcp and your wired network is also using dhcp then you could logically turn off the DHCP on the wireless system and have the computers obtain an address from your network.
If not send more information on your configuration and we can provide more information or guidance.
You haven't mentioned your other hardware models including whether your modem is just a modem or a modem/router. When setting up my system (many moons ago) I determined that putting the wireless router between the modem and switch (16-port) served two functions: it put an extra firewall between my network and the big bad world; and it allowed the router to handle all the DHCP.
Unless your modem also has router capabilities (some do, some don't) I believe you will need to install the new wireless modem ahead of the switch rather than behind it. In which case, it will likely not need any additional work to make it handle the whole network as it was likely designed to do.
u r confusing , a modem with a router . U might hv a wireless router/modem and a modem connected to a switch .
To access devices over a switch u hv to hv them on the same ip subnet . The dhcp u guys are talking depends on the modem which devices are picking up . Each modem has apool of roughly 50 internal ip addresses to be given to users .So there's a chance they might clash