cisco 1841 configuration

i recently bought a new cisco 1841 router. my ISP configured the router using the address 202.144.141.1 as a gateway….i can still access the internet for about 13 computers but i need to configure the internal address of my LAN starting from 192.168.0.1 as my router address….so that i can use 254 ip addresses in my LAN.
please give me the step by step method to configure my router……
looking for your help…..