How to change my ip address in windows 7

Are you on a router or directly off the modem?
If on a router you can reserve an IP in the DHCP settings or you can hardset the IP in windows 7 to an address within the range that the router uses.

If you are trying to change the IP of your modem, the only way to change it is to leave it unplugged for a long time and hopefully, but not always it MAY pick up a different IP than what it had before.