Can I ask what you are trying to achieve?
If you are trying to change your public IP, then this is down to your ISP and it's unlikely they will change this for you. Some ISP will give you a dynamic IP, others will give you a static IP. I have a static IP and I prefer this over dynamic.
If you are trying to change your internal router IP, then I have to ask why? If the router is also the DHCP server (most likely) then it will put all your local devices onto the same network range to communicate.