I wanna changed my IP?

when i follow tutorials on how to change IP via cmp it does work, but my modem which is a Motorola with Ethernet,DSL connection works fine, but i don't know if it doesn't recognizes the new IP so im not able to use internet. I open windows and i get them as if im not connected. Even though modem is working fine with all green lights on. Also i am using fire fox windows. I was ban from game so that why i wanna changed my IP.