Changing IP from your network or from the internet? If its from network then you need to ask your Network Admin on what IP is available and change that thru IP Protocol Properties under Local Area Connection Properties.
If its your internet IP then try disconnecting from your internet and maybe wait a couple of minutes. Usually you will get a new IP when you connect again. If not then try to wait a little longer then if you get the same IP try to ask your ISP why you are having the same IP over and over again.
why? wow...great answer...
If we knew what you're trying to accomplish, if would help us suggest a solution.