Login to the router. This can be done by directing to 192.168.1.1 (this number may differ depending on your type of router) in Internet Explorer for example. Use the default name/password if you have not set your own yet.
Step2
Unfortunately, there is no set view for routers. The look depends on the vendor. Whatever the case may be, direct to the page where DHCP, router IP, etc. are listed.
Step3
You can turn off the DHCP here. If this is done, you may have to set a static IP for the router, listing the DNS servers (provided by the ISP), as well as a gateway and subnet mask. For example, If your ISP provides you with an IP range of 230.12.0.0 - 230.12.255.255, then your subnet mask will be 255.255.0.0 and your gateway will be 230.12.0.1.