Changing my ip

So previously i have had to change my ip for various reasons. I'm not quite sure what i did before, but it worked, i think i changed my mac adress.

I want to change my computers ip without changing the router ip. how would i do this. I have googled around and i think i might have to release and renew in CMD but im not sure if my router is enabled with dhcp.

please help
-toto