HI i list the steps to be followed to change your ip in Windows XP .They are
1.Go to start--->run--->type cmd
2.Type ipconfig /release
3.Type ipconfig /renew
This will automatically change your ip address if it is dynamic ip.Else if you have static ip then you must contact your ISP to change it .After changing your ip visit Ip-Details.com to check that whether your network ip is changed or not .