You can't.
IP addresses are assigned by your ISP, and can only be changed by them. It is sometimes possible to change your IP by power cycling your router (because that disconnects your broadband connection and you will get an IP assigned from the ISP pool when you reconnect) but even then it's not definite that it won't be the same as last time.
There is some explanation (though not complete) here:
Using IP based Geolocation - and why it's pretty much useless.[
^]